Python 3.5 is shipped with Ubuntu 16.04, and it's the new stable
release. Add support for this runtime in tox. Note that Django 1.6 and
1.7 don't work with Python 3.5, so these are excluded.
Signed-off-by: Daniel Axtens <dja@axtens.net> Signed-off-by: Stephen Finucane <stephenfinucane@hotmail.com>