Fix DeprecationWarning running tests in Python 3.2+
Fix DeprecationWarning running tests in Python 3.2+

TestCase.assertRaisesRegexp was renamed to TestCase.assertRaisesRegex in
Python 3.2. six.assertRaisesRegex calls the appropriate method,
depending on the Python version.

Bouke/django-user-sessions,ivorbosloper/django-user-sessions,Bouke/django-user-sessions,ivorbosloper/django-user-sessions