Update packaging to 20.5

[pyup-bot]

This PR updates packaging from 20.3 to 20.5.

Changelog

20.5

~~~~~~~~~~~~~~~~~

* Officially support Python 3.9 (:issue:`343`)
* Deprecate the ``LegacyVersion`` and ``LegacySpecifier`` classes (:issue:`321`)
* Handle ``OSError`` on non-dynamic executables when attempting to resolve
the glibc version string.

20.4

~~~~~~~~~~~~~~~~~

* Canonicalize version before comparing specifiers. (:issue:`282`)
* Change type hint for ``canonicalize_name`` to return
``packaging.utils.NormalizedName``.
This enables the use of static typing tools (like mypy) to detect mixing of
normalized and un-normalized names.

Links

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

[pyup-bot]

Closing this in favor of #1384