Update twine to 3.1.0

[pyup-bot]

This PR updates twine from 2.0.0 to 3.1.0.

Changelog

3.1.0

* :feature:`547` Add support for specifying ``--non-interactive`` as an
environment variable.

3.0.0

* :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``

Links

• PyPI: https://pypi.org/project/twine
• Changelog: https://pyup.io/changelogs/twine/
• Docs: https://twine.readthedocs.io/