Bump sphinx from 2.3.0 to 2.3.1

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 2.3.0 to 2.3.1.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES)
- [Commits](sphinx-doc/sphinx@v2.3.0...v2.3.1)

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

setup.py

@@ -33,7 +33,7 @@
         'flake8-bugbear==19.8.0; python_version >= "3.5"',
         "pre-commit~=1.20",
     ],
-    "docs": ["Sphinx==2.3.0", "sphinx-issues==1.2.0", "sphinx-typlog-theme==0.8.0"]
+    "docs": ["Sphinx==2.3.1", "sphinx-issues==1.2.0", "sphinx-typlog-theme==0.8.0"]
     + FRAMEWORKS,
 }
 EXTRAS_REQUIRE["dev"] = EXTRAS_REQUIRE["tests"] + EXTRAS_REQUIRE["lint"] + ["tox"]