Bump flake8 from 3.9.0 to 3.9.1 (#27)

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[bot] <support@github.com>

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

setup.py

@@ -43,7 +43,7 @@ setup(
         'dev': [
             'nose==1.3.7',
             'coveralls==3.0.1',
-            'flake8==3.9.0'
+            'flake8==3.9.1'
         ]
     },
     zip_safe=False