Update pyflakes to 2.2.0
Changelog:
- Include column information in error messages
- Fix @overload detection with other decorators and in non-global scopes
- Fix return-type annotation being a class member
- Add check for f-strings without placeholders
- Improve python shebang detection
- Add support for assignment expressions (PEP 572)
- Make pyflakes more resistant to future syntax additions
- Fix false positives in partially quoted type annotations
- Switch from optparse to argparse
- Fix false positives in partially quoted type annotations in unusual contexts