Bump flake8 from 3.7.8 to 3.7.9 (#21)

Bumps [flake8](https://gitlab.com/pycqa/flake8) from 3.7.8 to 3.7.9.
- [Release notes](https://gitlab.com/pycqa/flake8/tags)
- [Commits](https://gitlab.com/pycqa/flake8/compare/3.7.8...3.7.9)

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

Author: dependabot-preview[bot]

requirements.txt

@@ -1,5 +1,5 @@
 entrypoints==0.3
-flake8==3.7.8
+flake8==3.7.9
 mccabe==0.6.1
 mypy==0.740
 pycodestyle==2.5.0