Update packaging to 21.0

[pyup-bot]

This PR updates packaging from 20.4 to 21.0.

Changelog

21.0

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

* `packaging` is now only compatible with Python 3.6 and above.
* Add support for zip files in ``parse_sdist_filename`` (:issue:`429`)

20.9

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

* Run `isort <https://pypi.org/project/isort/>`_ over the code base (:issue:`377`)
* Add support for the ``macosx_10_*_universal2`` platform tags (:issue:`379`)
* Introduce ``packaging.utils.parse_wheel_filename()`` and ``parse_sdist_filename()``
(:issue:`387` and :issue:`389`)

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 #490