Doesn't work on Python 3.8.x

[LWisteria]

As #267 (comment) reported

Note: Latest python3.8.x has numpy 1.18.x. Clpy issues compilation of numpy<=1.13.3, that fails with python3.8 (probably because of a variable rename, I don't know exactly), however, I successfully installed clpy in a python3.6 (as mentioned in README.md) on a virtualenv with numpy1.13.3.

[LWisteria]

As readme says, currently we specify the recommended systems including the python version.
And the reason why we specify the numpy version is #173 and etc, that's from our base version is old #33 .

Therefore, solving this problem should be a new feature request, not a (currently) bug. I'm welcome anyone to try and resolve.