Bump sphinx from 1.8.2 to 1.8.3 in /docs

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 1.8.2 to 1.8.3.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES)
- [Commits](sphinx-doc/sphinx@v1.8.2...v1.8.3)

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

docs/requirements.txt

@@ -1,7 +1,7 @@
 # This file is used to setup env
 # to generate documentation.
 
-sphinx==1.8.2
+sphinx==1.8.3
 sphinx_autodoc_typehints==1.6.0
 sphinx-click==1.4.1
 recommonmark==0.4.0