Bump packaging from 20.3 to 20.4

Bumps [packaging](https://github.com/pypa/packaging) from 20.3 to 20.4.
- [Release notes](https://github.com/pypa/packaging/releases)
- [Changelog](https://github.com/pypa/packaging/blob/master/CHANGELOG.rst)
- [Commits](pypa/packaging@20.3...20.4)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements.txt

@@ -1,7 +1,7 @@
 attrs==19.3.0
 importlib-metadata==1.6.1
 more-itertools==8.4.0
-packaging==20.3
+packaging==20.4
 parso==0.7.0
 pipdeptree==0.13.2
 pluggy==0.13.1