Adjust changes header

changes/bug15083

@@ -1,4 +1,4 @@
-  o Major bugfixes (relay, stability):
+  o Major bugfixes (relay, stability, possible security):
     - Fix a bug that could lead to a relay crashing with an assertion
       failure if a buffer of exactly the wrong layout was passed
       to buf_pullup() at exactly the wrong time. Fixes bug 15083;