Fix broken 1.7.3. It's 1.7.2 - 1.7.3 is documented but not yet on PyPI.

Author: tomchristie

tox.ini

@@ -13,7 +13,7 @@ deps =
        django14: Django==1.4.11  # Should track minimum supported
        django15: Django==1.5.6  # Should track minimum supported
        django16: Django==1.6.3  # Should track minimum supported
-       django17: Django==1.7.3  # Should track maximum supported
+       django17: Django==1.7.2  # Should track maximum supported
        djangomaster: https://github.com/django/django/zipball/master
        {py26,py27}-django{14,15,16,17}: django-guardian==1.2.3
        {py26,py27}-django{14,15,16}: oauth2==1.5.211