Taichi build on macOS with Python 3.6 to Python 3.8 covered #409

[Detavern]

Related issue id = #409

[Detavern]

Hi, as far as I know, python builds are not available on the macOS environment, which is same even using generic travis builds.

Currently, python version on osx depends on Xcode image version.

In my approach, homebrew and pyenv are used to build specific python version on macOS (quite tricky).

Additionally, since python 3.8, platform.platform() will use platform.mac_ver() instead.

# Python 3.6, 3.7
In [1]: import platform

In [2]: platform.platform()
Out[2]: 'Darwin-19.3.0-x86_64-i386-64bit'

# Python 3.8
In [1]: import platform

In [2]: platform.platform()
Out[2]: 'macOS-10.15.3-x86_64-i386-64bit'

Finally covered 🍺

[yuanming-hu]

Thank you so much!! This will help a lot of Mac users!