Add Django 2.2 and Python 3.8 to CI config

[bhrutledge]

Hi there! I'm crossing my fingers that this works, to support an upgrade that I'm currently doing. These seemed more expedient (and useful) than running the tests locally. That said, I've never used CircleCI, so it's possible it will break due to an error on my part.

The Django 2.2 jobs also use a more recent version of django-jinja for better compatibility (changelog)

[bhrutledge]

Looks like that's a no. @owais any insight or advice?

Also, I'm surprised to see the test-3.x-17 jobs in there, since they're not specified in config.yml.

[owais]

Looks like URLs in test app are not defined the way django 2.2 expects them to be.

[bhrutledge]

@owais Thanks for the tip! Looks like this is passing now, except for those mysterious test-*-17 jobs...

Side note: it was neat to use the CircleCI CLI to verify this locally:

$ circleci local execute --job test-3.6-22
    ...
----------------------------------------------------------------------
Ran 15 tests in 15.626s

OK
Destroying test database for alias 'default'...
Success!

[owais]

Thank you.