FIX: do not print root node in mhtree

src/mhtree/MHTree.java

@@ -174,10 +174,9 @@ public class MHTree extends Algorithm implements Serializable {
         return "MHTree{" +
                 "leafCapacity=" + leafCapacity +
                 ", arity=" + arity +
-                ", root=" + root +
-                ", insertType" + insertType +
-                ", objectToNodeDistance" + objectToNodeDistance +
-                ", nodeToNodeDistance" + nodeToNodeDistance +
+                ", insertType=" + insertType +
+                ", objectToNodeDistance=" + objectToNodeDistance +
+                ", nodeToNodeDistance=" + nodeToNodeDistance +
                 '}';
     }
 }