Add changelog entry for ocaml#1612

Author: voodoos

CHANGES.md

@@ -19,6 +19,7 @@ unreleased
     - Fix incorrect locations for string literals (#1574)
     - Fixed an issue that caused `errors` to erroneously alert about missing
       `cmi` files (#1577)
+    - Improve longident parsing (#1612, fixes #945)
   + editor modes
     - emacs: call the user's configured completion UI in
       `merlin-construct` (#1598)