[master] fix usage synopsis

trivial, not reviewed

src/bin/host/host.cc

@@ -232,7 +232,7 @@ main(int argc, char* argv[]) {
     argv += optind;
 
     if (argc < 1) {
-        cout << "Usage: host [-adprv] [-c class] [-t type] hostname [server]\n";
+        cout << "Usage: host [-adrv] [-c class] [-p port] [-t type] hostname [server]\n";
         exit(1);
     }