Update six to 1.14.0

[pyup-bot]

This PR updates six from 1.13.0 to 1.14.0.

Changelog

1.14.0

------

- Issue 288, pull request 289: Add `six.assertNotRegex`.

- Issue 317: `six.moves._dummy_thread` now points to the `_thread` module on
Python 3.9+. Python 3.7 and later requires threading and deprecated the
`_dummy_thread` module.

- Issue 308, pull request 314: Remove support for Python 2.6 and Python 3.2.

- Issue 250, issue 165, pull request 251: `six.wraps` now ignores missing
attributes. This follows the Python 3.2+ standard library behavior.

Links

• PyPI: https://pypi.org/project/six
• Changelog: https://pyup.io/changelogs/six/
• Repo: https://github.com/benjaminp/six