Bump sphinx from 3.4.3 to 3.5.4

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.4.3 to 3.5.4.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/4.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.4.3...v3.5.4)

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

setup.cfg

@@ -31,7 +31,7 @@ include_package_data = True
 
 [options.extras_require]
 dev =
-    Sphinx==3.4.3
+    Sphinx==3.5.4
     black==20.8b1
     bump2version==1.0.1
     flake8==3.8.4
@@ -45,7 +45,7 @@ dev =
     pytest-cov==2.11.1
     yamllint==1.26.0
 doc =
-    Sphinx==3.4.3
+    Sphinx==3.5.4
     furo==2020.12.30b24
 lint =
     black==20.8b1