Remove hard restriction for Django version in test requirements
Remove hard restriction for Django version in test requirements

This was silently forcing Django 1.6 to be installed in the Travis builds even
though environment variables were being used switch the Django version.

Signed-off-by: Byron Ruth <e9d71f5ee7c92d6dc9e92ffdad17b8bd49418f98@devel.io>

murphyke/avocado,murphyke/avocado,murphyke/avocado,murphyke/avocado