We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Pin vega version in requirements
To make sure things still work when ipyvega is updated (as it already has been)

--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `setup.py`
Content:
```
1 LONG_DESCRIPTION = """
2 Altair: A declarative statistical visualization library for Python.
3 
4 http://altair-viz.github.io/
5 
6 This package provides a Python API for building statistical visualizations
7 in a declarative manner. This API contains no actual visualization rendering
8 code, but instead emits JSON data structures following the `Vega-Lite`_
9 specification. For convenience, Altair can optionally use `ipyvega`_ to
10 seamlessly display client-side renderings in the Jupyter notebook.
11 
12 .. image:: https://raw.githubusercontent.com/altair-viz/altair/master/images/cars.png
13 
14 Please note that if you wish to use altair in the Jupyter Notebook, the
15 `ipyvega`_ notebook extension must be enabled as follows::
16 
17     $ pip install altair
18     $ pip install --upgrade notebook
19     $ jupyter nbextension install --sys-prefix --py vega
20 
21 See the `Altair Documentation`_ for tutorials, detailed installation
22 instructions, and examples.
23 See the `Altair Github Repository`_ for issues, bug reports, and contributions.
24 
25 .. _Altair Github Repository: http://github.com/altair-viz/altair/
26 .. _Altair Documentation: http://altair-viz.github.io/
27 .. _Vega-Lite: https://github.com/vega/vega-lite
28 .. _ipyvega: https://github.com/vega/ipyvega
29 """
30 
31 DESCRIPTION         = "Altair: A declarative statistical visualization library for Python."
32 NAME                = "altair"
33 PACKAGES            = ['altair',
34                        'altair.v1',
35                        'altair.v1.tests',
36                        'altair.v1.schema',
37                        'altair.v1.schema._interface',
38                        'altair.v1.schema._interface.tests',
39                        'altair.v1.examples',
40                        'altair.v1.examples.tests',
41                        'altair.datasets',
42                        'altair.datasets.tests',
43                        'altair.expr',
44                        'altair.expr.tests',
45                        'altair.tests',
46                        'altair.utils',
47                        'altair.utils.tests',
48                        ]
49 PACKAGE_DATA        = {'altair': ['notebooks/*.ipynb',
50                                   'notebooks/*.html',
51                                   'notebooks/auto_examples/*.ipynb',
52                                   'v1/schema/*.json',
53                                   'v1/examples/*.json',
54                                   'v1/examples/json/*.json',
55                                   'datasets/*.json',
56                                   'expr/*.json']}
57 AUTHOR              = "Brian E. Granger / Jake VanderPlas"
58 AUTHOR_EMAIL        = "ellisonbg@gmail.com / jakevdp@cs.washington.edu"
59 URL                 = 'http://altair-viz.github.io'
60 DOWNLOAD_URL        = 'http://github.com/altair-viz/altair/'
61 LICENSE             = 'BSD 3-clause'
62 INSTALL_REQUIRES    = ['traitlets>=4.3.1','ipython','pandas','vega>=0.4.4']
63 
64 
65 import io
66 import os
67 import re
68 
69 try:
70     from setuptools import setup
71 except ImportError:
72     from distutils.core import setup
73 
74 
75 def read(path, encoding='utf-8'):
76     path = os.path.join(os.path.dirname(__file__), path)
77     with io.open(path, encoding=encoding) as fp:
78         return fp.read()
79 
80 
81 def version(path):
82     """Obtain the packge version from a python file e.g. pkg/__init__.py
83 
84     See <https://packaging.python.org/en/latest/single_source_version.html>.
85     """
86     version_file = read(path)
87     version_match = re.search(r"""^__version__ = ['"]([^'"]*)['"]""",
88                               version_file, re.M)
89     if version_match:
90         return version_match.group(1)
91     raise RuntimeError("Unable to find version string.")
92 
93 
94 VERSION = version('altair/__init__.py')
95 
96 
97 setup(name=NAME,
98       version=VERSION,
99       description=DESCRIPTION,
100       long_description=LONG_DESCRIPTION,
101       author=AUTHOR,
102       author_email=AUTHOR_EMAIL,
103       url=URL,
104       download_url=DOWNLOAD_URL,
105       license=LICENSE,
106       packages=PACKAGES,
107       package_data=PACKAGE_DATA,
108       install_requires=INSTALL_REQUIRES,
109       classifiers=[
110         'Development Status :: 4 - Beta',
111         'Environment :: Console',
112         'Intended Audience :: Science/Research',
113         'License :: OSI Approved :: BSD License',
114         'Natural Language :: English',
115         'Programming Language :: Python :: 2.7',
116         'Programming Language :: Python :: 3.4',
117         'Programming Language :: Python :: 3.5'],
118      )
119
```

Path: `altair/__init__.py`
Content:
```
1 __version__ = '1.3.0.dev0'
2 
3 from .v1 import *
4
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/altair/__init__.py b/altair/__init__.py
--- a/altair/__init__.py
+++ b/altair/__init__.py
@@ -1,3 +1,3 @@
-__version__ = '1.3.0.dev0'
+__version__ = '1.2.1.dev0'
 
 from .v1 import *
diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -59,7 +59,7 @@
 URL                 = 'http://altair-viz.github.io'
 DOWNLOAD_URL        = 'http://github.com/altair-viz/altair/'
 LICENSE             = 'BSD 3-clause'
-INSTALL_REQUIRES    = ['traitlets>=4.3.1','ipython','pandas','vega>=0.4.4']
+INSTALL_REQUIRES    = ['traitlets>=4.3.1','ipython','pandas','vega==0.4.4']
 
 
 import io

{"golden_diff": "diff --git a/altair/__init__.py b/altair/__init__.py\n--- a/altair/__init__.py\n+++ b/altair/__init__.py\n@@ -1,3 +1,3 @@\n-__version__ = '1.3.0.dev0'\n+__version__ = '1.2.1.dev0'\n \n from .v1 import *\ndiff --git a/setup.py b/setup.py\n--- a/setup.py\n+++ b/setup.py\n@@ -59,7 +59,7 @@\n URL                 = 'http://altair-viz.github.io'\n DOWNLOAD_URL        = 'http://github.com/altair-viz/altair/'\n LICENSE             = 'BSD 3-clause'\n-INSTALL_REQUIRES    = ['traitlets>=4.3.1','ipython','pandas','vega>=0.4.4']\n+INSTALL_REQUIRES    = ['traitlets>=4.3.1','ipython','pandas','vega==0.4.4']\n \n \n import io\n", "issue": "Pin vega version in requirements\nTo make sure things still work when ipyvega is updated (as it already has been)\n", "before_files": [{"content": "LONG_DESCRIPTION = \"\"\"\nAltair: A declarative statistical visualization library for Python.\n\nhttp://altair-viz.github.io/\n\nThis package provides a Python API for building statistical visualizations\nin a declarative manner. This API contains no actual visualization rendering\ncode, but instead emits JSON data structures following the `Vega-Lite`_\nspecification. For convenience, Altair can optionally use `ipyvega`_ to\nseamlessly display client-side renderings in the Jupyter notebook.\n\n.. image:: https://raw.githubusercontent.com/altair-viz/altair/master/images/cars.png\n\nPlease note that if you wish to use altair in the Jupyter Notebook, the\n`ipyvega`_ notebook extension must be enabled as follows::\n\n    $ pip install altair\n    $ pip install --upgrade notebook\n    $ jupyter nbextension install --sys-prefix --py vega\n\nSee the `Altair Documentation`_ for tutorials, detailed installation\ninstructions, and examples.\nSee the `Altair Github Repository`_ for issues, bug reports, and contributions.\n\n.. _Altair Github Repository: http://github.com/altair-viz/altair/\n.. _Altair Documentation: http://altair-viz.github.io/\n.. _Vega-Lite: https://github.com/vega/vega-lite\n.. _ipyvega: https://github.com/vega/ipyvega\n\"\"\"\n\nDESCRIPTION         = \"Altair: A declarative statistical visualization library for Python.\"\nNAME                = \"altair\"\nPACKAGES            = ['altair',\n                       'altair.v1',\n                       'altair.v1.tests',\n                       'altair.v1.schema',\n                       'altair.v1.schema._interface',\n                       'altair.v1.schema._interface.tests',\n                       'altair.v1.examples',\n                       'altair.v1.examples.tests',\n                       'altair.datasets',\n                       'altair.datasets.tests',\n                       'altair.expr',\n                       'altair.expr.tests',\n                       'altair.tests',\n                       'altair.utils',\n                       'altair.utils.tests',\n                       ]\nPACKAGE_DATA        = {'altair': ['notebooks/*.ipynb',\n                                  'notebooks/*.html',\n                                  'notebooks/auto_examples/*.ipynb',\n                                  'v1/schema/*.json',\n                                  'v1/examples/*.json',\n                                  'v1/examples/json/*.json',\n                                  'datasets/*.json',\n                                  'expr/*.json']}\nAUTHOR              = \"Brian E. Granger / Jake VanderPlas\"\nAUTHOR_EMAIL        = \"ellisonbg@gmail.com / jakevdp@cs.washington.edu\"\nURL                 = 'http://altair-viz.github.io'\nDOWNLOAD_URL        = 'http://github.com/altair-viz/altair/'\nLICENSE             = 'BSD 3-clause'\nINSTALL_REQUIRES    = ['traitlets>=4.3.1','ipython','pandas','vega>=0.4.4']\n\n\nimport io\nimport os\nimport re\n\ntry:\n    from setuptools import setup\nexcept ImportError:\n    from distutils.core import setup\n\n\ndef read(path, encoding='utf-8'):\n    path = os.path.join(os.path.dirname(__file__), path)\n    with io.open(path, encoding=encoding) as fp:\n        return fp.read()\n\n\ndef version(path):\n    \"\"\"Obtain the packge version from a python file e.g. pkg/__init__.py\n\n    See <https://packaging.python.org/en/latest/single_source_version.html>.\n    \"\"\"\n    version_file = read(path)\n    version_match = re.search(r\"\"\"^__version__ = ['\"]([^'\"]*)['\"]\"\"\",\n                              version_file, re.M)\n    if version_match:\n        return version_match.group(1)\n    raise RuntimeError(\"Unable to find version string.\")\n\n\nVERSION = version('altair/__init__.py')\n\n\nsetup(name=NAME,\n      version=VERSION,\n      description=DESCRIPTION,\n      long_description=LONG_DESCRIPTION,\n      author=AUTHOR,\n      author_email=AUTHOR_EMAIL,\n      url=URL,\n      download_url=DOWNLOAD_URL,\n      license=LICENSE,\n      packages=PACKAGES,\n      package_data=PACKAGE_DATA,\n      install_requires=INSTALL_REQUIRES,\n      classifiers=[\n        'Development Status :: 4 - Beta',\n        'Environment :: Console',\n        'Intended Audience :: Science/Research',\n        'License :: OSI Approved :: BSD License',\n        'Natural Language :: English',\n        'Programming Language :: Python :: 2.7',\n        'Programming Language :: Python :: 3.4',\n        'Programming Language :: Python :: 3.5'],\n     )\n", "path": "setup.py"}, {"content": "__version__ = '1.3.0.dev0'\n\nfrom .v1 import *\n", "path": "altair/__init__.py"}], "after_files": [{"content": "LONG_DESCRIPTION = \"\"\"\nAltair: A declarative statistical visualization library for Python.\n\nhttp://altair-viz.github.io/\n\nThis package provides a Python API for building statistical visualizations\nin a declarative manner. This API contains no actual visualization rendering\ncode, but instead emits JSON data structures following the `Vega-Lite`_\nspecification. For convenience, Altair can optionally use `ipyvega`_ to\nseamlessly display client-side renderings in the Jupyter notebook.\n\n.. image:: https://raw.githubusercontent.com/altair-viz/altair/master/images/cars.png\n\nPlease note that if you wish to use altair in the Jupyter Notebook, the\n`ipyvega`_ notebook extension must be enabled as follows::\n\n    $ pip install altair\n    $ pip install --upgrade notebook\n    $ jupyter nbextension install --sys-prefix --py vega\n\nSee the `Altair Documentation`_ for tutorials, detailed installation\ninstructions, and examples.\nSee the `Altair Github Repository`_ for issues, bug reports, and contributions.\n\n.. _Altair Github Repository: http://github.com/altair-viz/altair/\n.. _Altair Documentation: http://altair-viz.github.io/\n.. _Vega-Lite: https://github.com/vega/vega-lite\n.. _ipyvega: https://github.com/vega/ipyvega\n\"\"\"\n\nDESCRIPTION         = \"Altair: A declarative statistical visualization library for Python.\"\nNAME                = \"altair\"\nPACKAGES            = ['altair',\n                       'altair.v1',\n                       'altair.v1.tests',\n                       'altair.v1.schema',\n                       'altair.v1.schema._interface',\n                       'altair.v1.schema._interface.tests',\n                       'altair.v1.examples',\n                       'altair.v1.examples.tests',\n                       'altair.datasets',\n                       'altair.datasets.tests',\n                       'altair.expr',\n                       'altair.expr.tests',\n                       'altair.tests',\n                       'altair.utils',\n                       'altair.utils.tests',\n                       ]\nPACKAGE_DATA        = {'altair': ['notebooks/*.ipynb',\n                                  'notebooks/*.html',\n                                  'notebooks/auto_examples/*.ipynb',\n                                  'v1/schema/*.json',\n                                  'v1/examples/*.json',\n                                  'v1/examples/json/*.json',\n                                  'datasets/*.json',\n                                  'expr/*.json']}\nAUTHOR              = \"Brian E. Granger / Jake VanderPlas\"\nAUTHOR_EMAIL        = \"ellisonbg@gmail.com / jakevdp@cs.washington.edu\"\nURL                 = 'http://altair-viz.github.io'\nDOWNLOAD_URL        = 'http://github.com/altair-viz/altair/'\nLICENSE             = 'BSD 3-clause'\nINSTALL_REQUIRES    = ['traitlets>=4.3.1','ipython','pandas','vega==0.4.4']\n\n\nimport io\nimport os\nimport re\n\ntry:\n    from setuptools import setup\nexcept ImportError:\n    from distutils.core import setup\n\n\ndef read(path, encoding='utf-8'):\n    path = os.path.join(os.path.dirname(__file__), path)\n    with io.open(path, encoding=encoding) as fp:\n        return fp.read()\n\n\ndef version(path):\n    \"\"\"Obtain the packge version from a python file e.g. pkg/__init__.py\n\n    See <https://packaging.python.org/en/latest/single_source_version.html>.\n    \"\"\"\n    version_file = read(path)\n    version_match = re.search(r\"\"\"^__version__ = ['\"]([^'\"]*)['\"]\"\"\",\n                              version_file, re.M)\n    if version_match:\n        return version_match.group(1)\n    raise RuntimeError(\"Unable to find version string.\")\n\n\nVERSION = version('altair/__init__.py')\n\n\nsetup(name=NAME,\n      version=VERSION,\n      description=DESCRIPTION,\n      long_description=LONG_DESCRIPTION,\n      author=AUTHOR,\n      author_email=AUTHOR_EMAIL,\n      url=URL,\n      download_url=DOWNLOAD_URL,\n      license=LICENSE,\n      packages=PACKAGES,\n      package_data=PACKAGE_DATA,\n      install_requires=INSTALL_REQUIRES,\n      classifiers=[\n        'Development Status :: 4 - Beta',\n        'Environment :: Console',\n        'Intended Audience :: Science/Research',\n        'License :: OSI Approved :: BSD License',\n        'Natural Language :: English',\n        'Programming Language :: Python :: 2.7',\n        'Programming Language :: Python :: 3.4',\n        'Programming Language :: Python :: 3.5'],\n     )\n", "path": "setup.py"}, {"content": "__version__ = '1.2.1.dev0'\n\nfrom .v1 import *\n", "path": "altair/__init__.py"}]}