RegexURLResolver usage

[jleclanche]

RegexURLResolver has been renamed in Django 2.1, this is causing failures on Travis.

One of the django devs noted that it's a private API and we could use url() instead.

[meshy]

I've addressed the rename in #318 (which is not yet ready to merge).

You've mentioned another way here -- if you know the details, could you please comment on the PR with your suggestion?

Many thanks.