change CHANGELOG

Former-commit-id: e76335a6ee5fadc0d72aabbed324822436b88ada

cpp/CHANGELOG.md

@@ -20,7 +20,7 @@ Please mark all change in change log and use the ticket from JIRA.
 - MS-22 - Enhancement for MemVector size control 
 - MS-92 - Unify behavior of debug and release build
 - MS-98 - Install all unit test to installation directory
-
+- MS-115 - Change is_startup of metric_config switch from true to on
 ## New Feature
 
 - MS-57 - Implement index load/search pipeline