Update pyflakes to 2.3.1

[pyup-bot]

This PR updates pyflakes from 2.2.0 to 2.3.1.

Changelog

2.3.1

- Fix regression in 2.3.0: type annotations no longer redefine imports

2.3.0

- Recognize tuple concatenation in ``__all__`` export definitions
- Better support use of annotation-only assignments when using
``from __future__ import annotations``
- Recognize special-case typing for ``Annotated``
- Fix undefined name ``__qualname__`` in class scope
- Recognize special-cased typing for ``TypeVar``
- Errors for undefined exports in ``__all__`` are shown in a deterministic order
- Fix false positives in certain typing constructs (``TypeVar``,
``NamedTuple``, ``TypedDict``, ``cast``)

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 #121