f35da80f27
Add Python 3.8 env in Travis CI test matrix. At present the pinning of flake8 disallows running of lint on Python 3.8 systems. Update flake8 ignore-list to ignore W504 instead of W503, the PEP guidance is that either is ok, but there must be local consistency. There are more occurences of binary operator before line-break than after in this repository, and we have also chosen to ignore W504 in most of our other repositories.