CHANGELOG update

docs/changelog.txt

@@ -163,7 +163,7 @@ mock 0.8.0 is the last version that will support Python 2.4.
 
 * `create_autospec` on the return value of a mock class will use `__call__`
   for the signature rather than `__init__`
-* Minor performance improvement instantiating `MagicMock`
+* Performance improvement instantiating `MagicMock`
 * Mocks used as magic methods have the same type as their parent instead of
   being hardcoded to `MagicMock`