Without this, using `configurations.setup()` after Django has been setup
already re-triggers the logging configuration, which then causes e.g.
pytest's caplog to not work anymore.
* Drop obsolete versions of Django from Travis tests
Django 1.8 reached EOL in April 2018.
Django 1.10 reached EOL in December 2017.
* Add support for testing Django 2.0 and 2.1 on Python 3.7
* Drop obsolete test (requires Django < 1.10)
- Drop django==1.9 as it reached end of life
- Drop python2.6, python3.3, and bring python3.6
- Bring django-2.0 in the matrix as expected failure until we add its
support
In Python 2.7+, unittest *is* unittest2. We prefer this one. But in
Python 2.6, we can get skipIf from django.utils.unittest, provided
Django is 1.8 or older.
