Previously Flake8 parsed both
max-line-length = 110
And
max_line_length = 110
From the config file without issue. When we updated our logic, I forgot
to test for that and we lost that behaviour temporarily.
Closes#152
If somebody explicitly has a `.flake8` file, presumably they intend to
put flake8 configuration in it, so prefer it to the generic `setup.cfg`
and `tox.ini` from pycodestyle.
