Fixed #21951 -- Updated docs to use __str__ for Python 3

Thanks Tim Graham for the report and recommendations

docs/ref/contrib/admin/actions.txt

@@ -57,8 +57,7 @@ simple news application with an ``Article`` model::
         body = models.TextField()
         status = models.CharField(max_length=1, choices=STATUS_CHOICES)
 
-        # On Python 3: def __str__(self):
-        def __unicode__(self):
+        def __str__(self):              # __unicode__ on Python 2
             return self.title
 
 A common task we might perform with a model like this is to update an