doc fix

Author: facontidavide

docs/tutorial_05_subtrees.md

@@ -96,7 +96,7 @@ int main()
     // This logger stores the execution time of each node
     MinitraceLogger logger_minitrace(tree.root_node, "bt_trace.json");
 
-#ifdef ZMQ_INSTALLED
+#ifdef ZMQ_FOUND
     // This logger publish status changes using ZeroMQ. Used by Groot
     PublisherZMQ publisher_zmq(tree);
 #endif