[2439] (minor) Comment fix

Fix a code in comment. It wouldn't work, but it was saying what not to
do anyway.

src/lib/python/isc/xfrin/tests/diff_tests.py

@@ -1098,7 +1098,7 @@ class DiffTest(unittest.TestCase):
             '''
             Empty init. The base class's __init__ can't be called,
             so we need to provide our own to shadow it -- and make sure
-            not to call the parent().__init__().
+            not to call the super().__init__().
             '''
             pass