Fixed spelling in comments

src/lb.cpp

@@ -102,8 +102,8 @@ int zmq::lb_t::send (msg_t *msg_)
         return -1;
     }
 
-    //  If it's final part of the message we can fluch it downstream and
-    //  continue round-robinning (load balance).
+    //  If it's final part of the message we can flush it downstream and
+    //  continue round-robining (load balance).
     more = msg_->flags () & msg_t::more? true: false;
     if (!more) {
         pipes [current]->flush ();