Bump flake8 in /{{cookiecutter.app_name}}/requirements

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>

{{cookiecutter.app_name}}/requirements/dev.txt

@@ -9,7 +9,7 @@ pdbpp==0.10.2
 
 # Lint and code style
 black==19.3b0
-flake8==3.7.8
+flake8==3.7.9
 flake8-blind-except==0.1.1
 flake8-debugger==3.2.0
 flake8-docstrings==1.5.0