Bump up maximum supported Django versions

Author: jpadilla

tox.ini

@@ -14,8 +14,8 @@ setenv =
 deps =
        django15: Django==1.5.6  # Should track minimum supported
        django16: Django==1.6.3  # Should track minimum supported
-       django17: Django==1.7.8  # Should track maximum supported
-       django18: Django==1.8.2  # Should track maximum supported
+       django17: Django==1.7.10  # Should track maximum supported
+       django18: Django==1.8.4  # Should track maximum supported
        djangomaster: https://github.com/django/django/archive/master.tar.gz
        -rrequirements/requirements-testing.txt
        -rrequirements/requirements-optionals.txt