docs: Fix external references to point to Django stable

@@ -288,5 +288,5 @@ epub_copyright = u'2013, Django Software Foundation and contributors'
 # Example configuration for intersphinx: refer to the Python standard library.
 intersphinx_mapping = {
     'python': ('http://docs.python.org/', None),
-    'django': ('http://docs.djangoproject.com/en/1.5', 'http://docs.djangoproject.com/en/1.5/_objects'),
+    'django': ('http://docs.djangoproject.com/en/stable', 'http://docs.djangoproject.com/en/stable/_objects'),
 }