Update packaging to 20.8

[pyup-bot]

This PR updates packaging from 20.4 to 20.8.

Changelog

20.8

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

* Revert back to setuptools for compatibility purposes for some Linux distros (:issue:`363`)
* Do not insert an underscore in wheel tags when the interpreter version number
is more than 2 digits (:issue:`372`)

20.7

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

No unreleased changes.

20.6

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

.. note:: This release was subsequently yanked, and these changes were included in 20.7.

* Fix flit configuration, to include LICENSE files (:issue:`357`)
* Make `intel` a recognized CPU architecture for the `universal` macOS platform tag (:issue:`361`)
* Add some missing type hints to `packaging.requirements` (issue:`350`)

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.

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 #426