Bump sphinx from 3.0.3 to 3.2.1

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.0.3 to 3.2.1.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/3.x/CHANGES)
- [Commits](https://github.com/sphinx-doc/sphinx/compare/v3.0.3...v3.2.1)

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

requirements-docs.txt

@@ -2,5 +2,5 @@
 -r requirements.txt
 
 # documentation generation support
-Sphinx==3.0.3
+Sphinx==3.2.1
 numpydoc==0.9.2