Project doesn't provide "Requires-Python" metadata.

[jaraco]

This project doesn't provide metadata for required Python versions and as a result, sdists and wheels for versions no longer supporting older Pythons still get installed on older Pythons:

$ python2 -m pip-run certifi -- -c pass
Collecting certifi
  Using cached certifi-2021.10.8-py2.py3-none-any.whl (149 kB)
Installing collected packages: certifi
Successfully installed certifi-2021.10.8

[hugovk]

This can be closed now #152 is merged.