Bump flake8 from 3.7.9 to 3.8.2 (#271)

Bumps [flake8](https://gitlab.com/pycqa/flake8) from 3.7.9 to 3.8.2.
- [Release notes](https://gitlab.com/pycqa/flake8/tags)
- [Commits](https://gitlab.com/pycqa/flake8/compare/3.7.9...3.8.2)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Author: dependabot-preview[bot]

tests/requirements.txt

@@ -1,6 +1,6 @@
 attrs==19.3.0
 coverage==5.1
-flake8==3.7.9
+flake8==3.8.2
 isort==4.3.21
 pycodestyle==2.5.0
 pyflakes==2.2.0