⬆️ Bump flake8 from 3.7.9 to 3.8.0 (#99)

Author: dependabot-preview[bot]

requirements_test.txt

@@ -1,6 +1,6 @@
 aresponses==2.0.0
 coverage==5.1
-flake8==3.7.9
+flake8==3.8.0
 flake8-docstrings==1.5.0
 isort==4.3.21
 mypy==0.770