Bump sphinx from 3.3.0 to 3.3.1

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.3.0 to 3.3.1.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/3.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.3.0...v3.3.1)

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

requirements/doc.txt

@@ -1,4 +1,4 @@
-sphinx==3.3.0
+sphinx==3.3.1
 sphinxcontrib-asyncio==0.3.0
 alabaster==0.7.12
 sphinx-autodoc-typehints==1.11.1