nox fails flake8 on fresh install

[vaneseltine]

https://github.com/openjournals/joss-reviews/issues/3440#issuecomment-939600112

A basic "nox" leads to flake8 reporting a bunch of style issues and then a bork. If someone wants to just see if the code tests work, I would advise devs to do

virtualenv .venv source .venv/bin/activate pip3 -r requirements/test.txt pytest

(which succeeds, I am pleased to note).