New flake8-bugbear version breaks stylecheck

[ftm]

Version 19.3.0 of flake8-bugbear introduced the new warnings B009 and B010 relating to the use of getattr() and setattr() with a constant, i.e. getattr(Input(), "input_type") (PyCQA/flake8-bugbear#55).

This is causing the CI to fail as that pattern is used 7 times in tests/test_widgets.py (see https://travis-ci.org/wtforms/wtforms/jobs/528390668 from #481 for an example failing build). The lines causing the issue are:

• https://github.com/wtforms/wtforms/blob/a4df965494232d3292abbfcf0498148be358f0a8/tests/test_widgets.py#L86
• https://github.com/wtforms/wtforms/blob/a4df965494232d3292abbfcf0498148be358f0a8/tests/test_widgets.py#L119
• https://github.com/wtforms/wtforms/blob/a4df965494232d3292abbfcf0498148be358f0a8/tests/test_widgets.py#L121
• https://github.com/wtforms/wtforms/blob/a4df965494232d3292abbfcf0498148be358f0a8/tests/test_widgets.py#L135-L137
• https://github.com/wtforms/wtforms/blob/a4df965494232d3292abbfcf0498148be358f0a8/tests/test_widgets.py#L156