update changelog

docs/Changelog.md

@@ -39,6 +39,7 @@ sending a mail to <afl-users+subscribe@googlegroups.com>.
   - utils/aflpp_driver:
     - aflpp_qemu_driver_hook fixed to work with qemu_mode
     - aflpp_driver now compiled with -fPIC
+  - updated the grammar custom mutator to the newest version
   - add -d (add dead fuzzer stats) to afl-whatsup
 
 ### Version ++3.12c (release)