Bump sphinx from 3.1.1 to 3.1.2

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.1.1 to 3.1.2.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/3.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.1.1...v3.1.2)

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

Author: dependabot-preview[bot]

requirements-dev.txt

@@ -13,5 +13,5 @@ pytest-cov==2.10.0
 pytest==5.4.3
 pytorch_ranger==0.1.1
 sphinx-autodoc-typehints==1.11.0
-sphinx==3.1.1
+sphinx==3.1.2
 torch==1.5.1