Bump hypothesis from 5.19.1 to 5.20.3 in /src/requirements (#594)

Bumps [hypothesis](https://github.com/HypothesisWorks/hypothesis) from 5.19.1 to 5.20.3.
- [Release notes](https://github.com/HypothesisWorks/hypothesis/releases)
- [Commits](https://github.com/HypothesisWorks/hypothesis/compare/hypothesis-python-5.19.1...hypothesis-python-5.20.3)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

src/requirements/dev.txt

@@ -7,5 +7,5 @@ codecov==2.1.7
 black==19.10b0
 pre-commit==2.6.0
 isort==5.1.1
-hypothesis==5.19.1
+hypothesis==5.20.3
 flake8==3.8.3