python 3 fixes

changes made as suggested

lms/djangoapps/rss_proxy/models.py

@@ -5,9 +5,11 @@ from __future__ import absolute_import
 
 import six
 from django.db import models
+from django.utils.encoding import python_2_unicode_compatible
 from model_utils.models import TimeStampedModel
 
 
+@python_2_unicode_compatible
 class WhitelistedRssUrl(TimeStampedModel):
     """
     Model for persisting RSS feed URLs which are whitelisted
@@ -21,5 +23,5 @@ class WhitelistedRssUrl(TimeStampedModel):
         """ Meta class for this Django model """
         app_label = "rss_proxy"
 
-    def __unicode__(self):
+    def __str__(self):
         return six.text_type(self.url)