Concurrency Modification Error Fixed

We were getting a concurrency Modification error on the treemap because multiple operations may have been accessing the RoutingTable's getAllNodes() method at once.
- Fixed it by making this method synchronized.

src/kademlia/routing/RoutingTable.java

@@ -183,7 +183,7 @@ public class RoutingTable implements KadRoutingTable
      * @return List A List of all Nodes in this RoutingTable
      */
     @Override
-    public final List getAllNodes()
+    public synchronized final List getAllNodes()
     {
         List<Node> nodes = new ArrayList<>();