Merge pull request #1168 from adamtheturtle/dependabot/pip/sphinx-substitution-extensions-2020.2.21.0

Bump sphinx-substitution-extensions from 2019.12.28.0 to 2020.2.21.0

Author: adamtheturtle

dev-requirements.txt

@@ -2,7 +2,7 @@
 # because Read The Docs needs a requirements file.
 PyYAML==5.3
 Pygments==2.5.2
-Sphinx-Substitution-Extensions==2019.12.28.0
+Sphinx-Substitution-Extensions==2020.2.21.0
 Sphinx==2.4.3
 VWS-Python-Mock==2019.12.27.0
 VWS-Test-Fixtures==2019.12.13.1