Make attribute final

Author: oschwald

src/main/java/com/maxmind/db/Networks.java

@@ -145,7 +145,7 @@ public boolean hasNext()  {
 
     static class NetworkNode {
         /** The IP address of the node. */
-        public byte[] ip;
+        public final byte[] ip;
         /** The prefix of the node. */
         public int prefix;
         /** The node number. */