Update CHANGES.txt for commit of YARN-4348 to branch-2.7 and branch-2.6.

hadoop-yarn-project/CHANGES.txt

@@ -2029,6 +2029,9 @@ Release 2.6.3 - UNRELEASED
     YARN-4365. FileSystemNodeLabelStore should check for root dir existence on
     startup (Kuhu Shukla via jlowe)
 
+    YARN-4348. ZKRMStateStore.syncInternal shouldn't wait for sync completion for
+    avoiding blocking ZK's event thread. (ozawa)
+
 Release 2.6.2 - 2015-10-28
 
   INCOMPATIBLE CHANGES