Refactors the Travis workflow to use miniconda on macOS and Linux. Before, macOS used pyenv and Linux used what came on the Travis build image. Using miniconda for both makes the workflow more consistent and should be easier to debug in the future. It makes the Linux builds take slightly (1-2 minutes) longer, but the build times have always dominated by the macOS tests, and those are much faster. Consider three Travis builds:
We also drop test coverage for Python 3.5, which is at end of life. This allows us to clean up the workflow a bit, since black was not supported on Python 3.5.
Resolves #301.
This does two things:
black
was not supported on Python 3.5.