Small cleanup

src/main/java/com/google/code/gossip/event/GossipState.java

@@ -2,8 +2,8 @@ package com.google.code.gossip.event;
 
 public enum GossipState {
   UP("up"), DOWN("down");
-  private String state;
-  
+  private final String state;
+
   private GossipState(String state){
     this.state = state;
   }