Bump flake8 from 3.7.7 to 3.7.8

Bumps [flake8](https://gitlab.com/pycqa/flake8) from 3.7.7 to 3.7.8.
- [Release notes](https://gitlab.com/pycqa/flake8/tags)
- [Commits](https://gitlab.com/pycqa/flake8/compare/3.7.7...3.7.8)

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

Pipfile

@@ -10,7 +10,7 @@ pytest = "*"
 
 [dev-packages]
 coveralls = "==1.7.0"
-flake8 = "==3.7.7"
+flake8 = "==3.7.8"
 flake8-docstrings = "==1.3.0"
 flake8-isort = "==2.7.0"
 pytest = "==4.4.0"