flake8 3.6 breaks with our configuration

[effigies]

A number of errors are suddenly appearing. It seems pycodestyle has introduced new errors and flake8 has introduced new syntax for updating the ignore list as opposed to replacing it.

• https://gitlab.com/pycqa/flake8/issues/463
• https://gitlab.com/pycqa/flake8/issues/466

If somebody has time, going through and seeing which are things worth conforming to, ignoring in individual files, and ignoring in the whole project would probably be a good idea. I don't really want to have to constrain style checkers.

The short term solution is probably just to pin to flake8<3.6.