Update pyflakes to 2.0.0

[pyup-bot]

This PR updates pyflakes from 1.5.0 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(...)`

1.6.0

- Process function scope variable annotations for used names
- Find Python files without extensions by their shebang

Links

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

[pyup-bot]

Closing this in favor of #82