Fix shared_db_wrapper tests on Python 2.7

Author: ktosiek

tests/test_database.py

@@ -54,7 +54,7 @@ def test_noaccess_fixture(noaccess):
 
 @pytest.mark.skipif(get_django_version() < (1, 6),
                     reason="shared_db_wrapper needs at least Django 1.6")
-class TestSharedDbWrapper:
+class TestSharedDbWrapper(object):
     """Tests for sharing data created with share_db_wrapper, order matters."""
     @pytest.fixture(scope='class')
     def shared_item(self, request, shared_db_wrapper):