Add missing entry in CHANGES.txt for HDFS-6757.

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -533,6 +533,8 @@ Release 2.8.0 - UNRELEASED
     HDFS-8113. Add check for null BlockCollection pointers in
     BlockInfoContiguous structures (Chengbing Liu via Colin P. McCabe)
 
+    HDFS-6757. Simplify lease manager with INodeID. (wheat9)
+
   OPTIMIZATIONS
 
     HDFS-8026. Trace FSOutputSummer#writeChecksumChunks rather than