Bump mkdocs-material from 3.3.0 to 4.0.1 in /requirements

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 3.3.0 to 4.0.1.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@3.3.0...4.0.1)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot-support

requirements/docs.txt

@@ -3,5 +3,5 @@
 # This file is used by Read the Docs, Travis and when building locally.
 
 mkdocs==1.0.4
-mkdocs-material==3.3.0
+mkdocs-material==4.0.1
 mdx_truly_sane_lists==1.2