py-six: updated to 1.14.0

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.

(adam)