Fix CHANGES.txt. Credit Mayank Bansal for his contributions on YARN-2459

hadoop-yarn-project/CHANGES.txt

@@ -312,7 +312,7 @@ Release 2.6.0 - UNRELEASED
     (Zhihai Xu via kasha)
 
     YARN-2459. RM crashes if App gets rejected for any reason 
-    and HA is enabled. (Jian He via xgong)
+    and HA is enabled. (Jian He and Mayank Bansal via xgong)
 
     YARN-2158. Fixed TestRMWebServicesAppsModification#testSingleAppKill test
     failure. (Varun Vasudev via jianhe)