Add support for Django 2.0

[jeancochrane]

Overview

This PR adds support for Django 2.0.

Notes

• This PR branches off of Remove djsonb dependency and move its relevant logic into Grout core #7.
• Initially we hoped to support unreleased development versions of Django in order to stay ahead of the curve. However, as outlined in that link, we can only support Django 2.0 for now because of a dependency conflict between Python 2 and django-filter.

Testing

Travis will run unit tests for all supported versions of Python and Django. To run them locally:

./scripts/test app

Note that this will install virtualenvs for every version of Python and Django in the support matrix. If you'd like to remove virtualenvs after you're done, make sure to run sudo rm -Rf .tox in the project directory.

Closes azavea/grout-2018-fellowship#27.

[flibbertigibbet]

👍

Glad to see it looks like the required changes were pretty straightforward!