have version implement serializable to DiscoveryNode can be serialized

src/main/java/org/elasticsearch/Version.java

@@ -25,10 +25,11 @@ import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.monitor.jvm.JvmInfo;
 
 import java.io.IOException;
+import java.io.Serializable;
 
 /**
  */
-public class Version {
+public class Version implements Serializable {
 
     // The logic for ID is: XXYYZZAA, where XX is major version, YY is minor version, ZZ is revision, and AA is Beta/RC indicator
     // AA values below 50 are beta builds, and below 99 are RC builds, with 99 indicating a release