- Update deps to really match up reality

- version update to 3.1.1
bug`548` Restore --non-interactive as a flag not expecting an argument.
:feature:`547` Add support for specifying --non-interactive as an environment variable.
:feature:`336` When a client certificate is indicated, all password processing is disabled.
:feature:`489` Add --non-interactive flag to abort upload rather than interactively prompt if credentials are missing.
:feature:`524` Twine now unconditionally requires the keyring library and no longer supports uninstalling keyring as a means to disable that functionality. Instead, use keyring --disable keyring functionality if necessary.
:feature:`518` Add Python 3.8 to classifiers.
bug`332 major` More robust handling of server response in --skip-existing
:feature:`437` Twine now requires Python 3.6 or later. Use pip 9 or pin to "twine<2" to install twine on older Python versions.
bug`491 major` Require requests 2.20 or later to avoid reported security vulnerabilities in earlier releases.
- python3 only package

- Fix build without python2