Versions from 0.23.4 to  0.25.1 fail to install on Alpine Linux 

#### Problem description
already have installed numpy==1.17.1

but installation of pandas > 0.23.4 fails with 
```
ERROR: Command errored out with exit status 1:
     command: /usr/local/bin/python -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-hmmx65yg/pandas/setup.py'"'"'; __file__='"'"'/tmp/pip-install-hmmx65yg/pandas/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base pip-egg-info
         cwd: /tmp/pip-install-hmmx65yg/pandas/
    Complete output (18 lines):
    Traceback (most recent call last):
      File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 359, in get_provider
        module = sys.modules[moduleOrReq]
    KeyError: 'numpy'
    
    During handling of the above exception, another exception occurred:
    
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-install-hmmx65yg/pandas/setup.py", line 732, in <module>
        ext_modules=maybe_cythonize(extensions, compiler_directives=directives),
      File "/tmp/pip-install-hmmx65yg/pandas/setup.py", line 475, in maybe_cythonize
        numpy_incl = pkg_resources.resource_filename('numpy', 'core/include')
      File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 1144, in resource_filename
        return get_provider(package_or_requirement).get_resource_filename(
      File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 361, in get_provider
        __import__(moduleOrReq)
    ModuleNotFoundError: No module named 'numpy'
    ----------------------------------------
ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.
```
