Bump flake8 from 3.8.3 to 3.8.4 (#42)

Bumps [flake8](https://gitlab.com/pycqa/flake8) from 3.8.3 to 3.8.4.
- [Release notes](https://gitlab.com/pycqa/flake8/tags)
- [Commits](https://gitlab.com/pycqa/flake8/compare/3.8.3...3.8.4)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements.txt

@@ -1,5 +1,5 @@
 entrypoints==0.3
-flake8==3.8.3
+flake8==3.8.4
 mccabe==0.6.1
 mypy==0.782
 pycodestyle==2.6.0