fix trivial typo in example's comment

Fix comment in accordance with the original type description from the:
`boost/interprocess/creation_tags.hpp`.

Signed-off-by: Gluttton <gluttton@ukr.net>

example/comp_doc_message_queueB.cpp

@@ -20,7 +20,7 @@ int main ()
    try{
       //Open a message queue.
       message_queue mq
-         (open_only        //only create
+         (open_only        //only open
          ,"message_queue"  //name
          );