[1.8.x] Fixed typos in code comments.

Backport of 039465a6a7 from master

tests/basic/tests.py

@@ -357,7 +357,7 @@ class ModelTest(TestCase):
         Article.objects.create(headline=lazy, pub_date=datetime.now())
         article = Article.objects.get()
         self.assertEqual(article.headline, notlazy)
-        # test that assign + save works with Promise objecs
+        # test that assign + save works with Promise objects
         article.headline = lazy
         article.save()
         self.assertEqual(article.headline, notlazy)