Bump sphinx from 3.1.0 to 3.1.1 (#274)

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.1.0 to 3.1.1.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/3.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.1.0...v3.1.1)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

requirements-dev.txt

@@ -3,5 +3,5 @@ wheel==0.34.2
 twine==3.1.1
 restructuredtext_lint==1.3.1
 unittest-xml-reporting==3.0.2
-sphinx==3.1.0
+sphinx==3.1.1
 sphinx-rtd-theme==0.4.3