Pylint requirements don't work on Python 3.7

[PeterJCLaw]

It turns out that PEP 479 breaks Pylint < 2 (see pylint-dev/pylint@1448b32), meaning that Python 3.7+ needs Pylint 2+ . However, Pylint 2+ is only available on Python 3.4+.

The net result of this is that there isn't a version of Pylint which works on both Python 2.7 and Python 3.7+.

Since for the moment we need to keep Python 2.7 working, this is essentially blocked, however is worth recording now we know what the issue is.