Update sphinx from 2.2.1 to 2.3.1 (#58)

Co-authored-by: Lev Rubel <rubel.lev@gmail.com>

Author: 2 people

requirements_dev.txt

@@ -2,7 +2,7 @@ pip==19.3.1
 bumpversion==0.5.3
 wheel==0.33.6
 watchdog==0.9.0
-Sphinx==2.2.1
+Sphinx==2.3.1
 twine==3.1.1
 
 fastapi==0.42.0