Bump pyflakes from 2.1.1 to 2.2.0

Bumps [pyflakes](https://github.com/PyCQA/pyflakes) from 2.1.1 to 2.2.0.
- [Release notes](https://github.com/PyCQA/pyflakes/releases)
- [Changelog](https://github.com/PyCQA/pyflakes/blob/master/NEWS.rst)
- [Commits](https://github.com/PyCQA/pyflakes/compare/2.1.1...2.2.0)

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

requirements-dev.txt

@@ -2,7 +2,7 @@ coverage
 mock
 nose
 pycodestyle==2.5.0
-pyflakes==2.1.1
+pyflakes==2.2.0
 readme_renderer[md]==26.0
 requests_mock
 twine==1.15.0