fix memory zone build error which caused by rbtree interface change

src/lib/datasrc/memory_datasrc.cc

@@ -192,7 +192,7 @@ struct MemoryZone::MemoryZoneImpl {
         // Get the node
         DomainNode* node(NULL);
         FindState state(options);
-        NodeChain<Domain> node_path;
+        RBTreeNodeChain<Domain> node_path;
         switch (domains_.find(name, &node, node_path, zonecutCallback, &state)) {
             case DomainTree::PARTIALMATCH:
                 if (state.zonecut_node_ != NULL) {