Log Message:
py-flakes: updated to 2.1.0

Release 2.1.0
- Allow intentional assignment to variables named _
- Recognize __module__ as a valid name in class scope
- pyflakes.checker.Checker supports checking of partial ast trees
- Detect assign-before-use for local variables which shadow builtin names
- Detect invalid print syntax using >> operator
- Treat async for the same as a for loop for introducing variables
- Add detection for list concatenation in __all__
- Exempt @typing.overload from duplicate function declaration
- Importing a submodule of an as-aliased import-import is marked as
  used
- Report undefined names from __all__ as possibly coming from a *
  import
- Add support for changes in Python 3.8-dev
- Add support for PEP 563 (from __future__ import annotations)
- Include Python version and platform information in pyflakes --version
- Recognize __annotations__ as a valid magic global in Python 3.6+
- Mark names used in PEP 484 # type: ... comments as used
- Add check for use of is operator with str, bytes, and int
  literals