Analogous to gitpython-developers/gitdb#94,
this brings back Python 3.7 support (allowing it to be installed on
3.7, and testing on 3.7), even though 3.7 is end of life, because
support for 3.7 is not being dropped by GitPython (or gitdb) yet,
and there is value in keeping GitPython, gitdb, and smmap
consistent.

This reverts commit f1b4d14.

marked this pull request as ready for review

This was referenced