Tons of Test Errors with 0.20.3 and 0.21.0.dev0 Python 3.6.3
#### Code Sample, a copy-pastable example if possible

```python
nosetests -v pandas

```
#### Problem description

I installed 0.20.3 and then also tried 0.21.0.dev0 and there are a ton of tests that fail for both versions on python3.6.3.

#### Expected Output
All tests passing, I suppose.
#### Output of ``pd.show_versions()``

[paste the output of ``pd.show_versions()`` here below this line]

>>> pd.show_versions()

INSTALLED VERSIONS
------------------
commit: None
python: 3.6.3.final.0
python-bits: 64
OS: Linux
OS-release: 3.19.0-32-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.21.0.dev
pytest: 3.2.3
pip: 9.0.1
setuptools: 36.5.0
Cython: 0.27.1
numpy: 1.13.3
scipy: 0.19.1
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.6.0
pytz: 2017.2
blosc: None
bottleneck: 1.2.1
tables: 3.4.2
numexpr: 2.6.4
feather: None
matplotlib: 2.1.0
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
sqlalchemy: 1.1.14
pymysql: None
psycopg2: None
jinja2: None
s3fs: None
pandas_gbq: None
pandas_datareader: None

[pandas_dev.txt](https://github.com/pandas-dev/pandas/files/1367499/pandas_dev.txt)
