PIG-5157: Adding missing entry in CHANGES.txt

git-svn-id: https://svn.apache.org/repos/asf/pig/trunk@1802674 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/CHANGES.txt b/CHANGES.txt
index 13fc9e9..3540884 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -24,6 +24,8 @@
  
 IMPROVEMENTS
 
+PIG-5157: Upgrade to Spark 2.0 (nkollar via liyunzhang)
+
 PIG-5237: Fix DOT file parsing to enable DOT-based physical plan testing (YaShock via szita)
 
 PIG-5269: MapReduceLauncher and MRJobStats imports org.python.google.common.collect.Lists instead of org.google.common.collect.Lists (nkollar via szita)