Merge pull request #57 from edx/clintonb/abstract-model-fix

Fixed abstract model declaration

course_discovery/apps/course_metadata/models.py

@@ -42,6 +42,9 @@ class AbstractMediaModel(TimeStampedModel):
     def __str__(self):
         return self.src
 
+    class Meta(object):
+        abstract = True
+
 
 class Image(AbstractMediaModel):
     """ Image model. """