tox: Update pyflakes to 1.0.0.
tox: Update pyflakes to 1.0.0.

Changes:

- Don't mark shadowing variable as 'used'.
- Test that used variable in loop is considered used
- Don't report UnusedImport when binding global name
- Support Python 3.5 async/await statements for Pyflakes.
- Use os.linesep for Windows compatibility
- os.chmod() supports only read-only flag operations on Windows

The-Compiler/pytest-mccabe