Bump flake8 from 3.9.0 to 3.9.1

Bumps [flake8](https://gitlab.com/pycqa/flake8) from 3.9.0 to 3.9.1.
- [Release notes](https://gitlab.com/pycqa/flake8/tags)
- [Commits](https://gitlab.com/pycqa/flake8/compare/3.9.0...3.9.1)

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

setup.py

@@ -5,7 +5,7 @@
 EXTRAS_REQUIRE = {
     "tests": ["pytest"],
     "lint": [
-        "flake8==3.9.0",
+        "flake8==3.9.1",
         "flake8-bugbear==20.11.1",
         "pre-commit~=2.7",
     ],