Bump flake8 from 3.7.1 to 3.7.3 in /{{cookiecutter.app_name}}

Bumps [flake8](https://gitlab.com/pycqa/flake8) from 3.7.1 to 3.7.3.
- [Release notes](https://gitlab.com/pycqa/flake8/tags)
- [Commits](https://gitlab.com/pycqa/flake8/compare/3.7.1...3.7.3)

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

{{cookiecutter.app_name}}/Pipfile

@@ -50,7 +50,7 @@ WebTest = "==2.0.32"
 factory-boy = "==2.11.*"
 
 # Lint and code style
-flake8 = "==3.7.1"
+flake8 = "==3.7.3"
 flake8-blind-except = "==0.1.1"
 flake8-debugger = "==3.1.0"
 flake8-docstrings = "==1.3.0"