Bump typing-extensions from 3.7.2 to 3.7.4 in /docs (#100)

Bumps [typing-extensions](https://github.com/python/typing) from 3.7.2 to 3.7.4.
- [Release notes](https://github.com/python/typing/releases)
- [Commits](https://github.com/python/typing/commits/3.7.4)

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

Author: dependabot-preview[bot]

docs/requirements.txt

@@ -10,4 +10,4 @@ m2r==0.2.1
 tomlkit==0.5.3
 
 # Dependencies of our project:
-typing-extensions==3.7.2
+typing-extensions==3.7.4