Update pyflakes to 2.0.0

[pyup-bot]

This PR updates pyflakes from 1.6.0 to 2.0.0.

Changelog

2.0.0

- Drop support for EOL Python <2.7 and 3.2-3.3
- Check for unused exception binding in `except:` block
- Handle string literal type annotations
- Ignore redefinitions of `_`, unless originally defined by import
- Support `__class__` without `self` in Python 3
- Issue an error for `raise NotImplemented(...)`

Links

• PyPI: https://pypi.org/project/pyflakes
• Changelog: https://pyup.io/changelogs/pyflakes/
• Repo: https://github.com/PyCQA/pyflakes

[coveralls]

Coverage remained the same at 44.828% when pulling 4725fca on pyup-update-pyflakes-1.6.0-to-2.0.0 into 9e0c446 on master.