Fix changes file for 20864: 20638 _did_ get into 0.2.9

changes/bug20864

@@ -1,4 +1,4 @@
-  o Minor bugfixes (hidden services):
+  o Minor bugfixes (unit tests, hidden services):
     - Remove a double-free in the single onion service unit test. Stop
       ignoring a return value. Make future changes less error-prone.
-      Fixes bug 20864; bugfix on 20638; not in any released version of tor.
+      Fixes bug 20864; bugfix on 0.2.9.6-rc.