Bump hypothesis from 6.7.0 to 6.8.0 in /docs

Bumps [hypothesis](https://github.com/HypothesisWorks/hypothesis) from 6.7.0 to 6.8.0.
- [Release notes](https://github.com/HypothesisWorks/hypothesis/releases)
- [Commits](HypothesisWorks/hypothesis@hypothesis-python-6.7.0...hypothesis-python-6.8.0)

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

Author: dependabot-preview[bot]

docs/requirements.txt

@@ -15,4 +15,4 @@ pygments==2.8.1
 typing-extensions==3.7.4.3
 mypy==0.812
 pytest==6.2.2
-hypothesis==6.7.0
+hypothesis==6.8.0