Update CHANGES.txt to reflect commit of MR-5982 to 2.7.2

hadoop-mapreduce-project/CHANGES.txt

@@ -565,9 +565,6 @@ Release 2.8.0 - UNRELEASED
     MAPREDUCE-5002. AM could potentially allocate a reduce container to a map
     attempt (Chang Li via jlowe)
 
-    MAPREDUCE-5982. Task attempts that fail from the ASSIGNED state can
-    disappear (Chang Li via jlowe)
-
 Release 2.7.2 - UNRELEASED
 
   INCOMPATIBLE CHANGES
@@ -606,6 +603,9 @@ Release 2.7.2 - UNRELEASED
     position/key information for uncompressed input sometimes. (Zhihai Xu via
     jlowe)
 
+    MAPREDUCE-5982. Task attempts that fail from the ASSIGNED state can
+    disappear (Chang Li via jlowe)
+
 Release 2.7.1 - 2015-07-06 
 
   INCOMPATIBLE CHANGES