pyproj: pypi installation errors

cc @justb4

Via https://github.com/geopython/GeoHealthCheck/issues/240, looks like with the latest pyproj release on pypi there are install issues:

Downloading/unpacking OWSLib==0.17.0
  Downloading OWSLib-0.17.0.tar.gz (149kB): 149kB downloaded
  Running setup.py (path:/tmp/pip_build_kralidist/OWSLib/setup.py) egg_info for package OWSLib

    warning: manifest_maker: MANIFEST.in, line 3: 'recursive-include' expects <dir> <pattern1> <pattern2> ...

Downloading/unpacking python-dateutil>=1.5 (from OWSLib==0.17.0)
  Downloading python_dateutil-2.8.0-py2.py3-none-any.whl (226kB): 226kB downloaded
Downloading/unpacking pytz (from OWSLib==0.17.0)
  Downloading pytz-2018.9-py2.py3-none-any.whl (510kB): 510kB downloaded
Requirement already satisfied (use --upgrade to upgrade): requests>=1.0 in /usr/lib/python2.7/dist-packages (from OWSLib==0.17.0)
Downloading/unpacking pyproj (from OWSLib==0.17.0)
  Downloading pyproj-2.0.0.tar.gz (408kB): 408kB downloaded
  Running setup.py (path:/tmp/pip_build_kralidist/pyproj/setup.py) egg_info for package pyproj
    ERROR: Cython.Build.cythonize not found. Cython is required to build from a repo.
    Complete output from command python setup.py egg_info:
    ERROR: Cython.Build.cythonize not found. Cython is required to build from a repo.

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Cleaning up...
Command python setup.py egg_info failed with error code 1 in /.....