reverted protobuf.version to 2.5.0

Author: kiran-maturi

hadoop-project/pom.xml

@@ -85,7 +85,7 @@
     <re2j.version>1.1</re2j.version>
 
     <!--Protobuf version for backward compatibility-->
-    <protobuf.version>3.7.1</protobuf.version>
+    <protobuf.version>2.5.0</protobuf.version>
     <!-- ProtocolBuffer version, actually used in Hadoop -->
     <hadoop.protobuf.version>3.7.1</hadoop.protobuf.version>
     <protoc.path>${env.HADOOP_PROTOC_PATH}</protoc.path>