Bumps [flake8](https://gitlab.com/pycqa/flake8) from 3.6.0 to 3.8.1.
- [Release notes](https://gitlab.com/pycqa/flake8/tags)
- [Commits](https://gitlab.com/pycqa/flake8/compare/3.6.0...3.8.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>