[Changelog] update Changelog w.r.t. !2221

Changelog

@@ -17,6 +17,8 @@
 Open Source Release <next-release>
 ##################################
 
+-*  Obfuscator [2019/04/09] Also obfuscate formals in function pointer types.
+              Fixes #2433.
 -   Inout     [2019/04/01] Fix performance issue when initializing large arrays.
 -   ACSL      [2019/03/08] Add check annotation, similar to assert except that
               it does not introduce additional hypotheses on the program state