Update Worker.php

Worker.php

@@ -810,7 +810,7 @@ class Worker
                 posix_kill($master_pid, $sig);
                 exit;
             default :
-		echo 'Unknow command: ' . $command . '\n';
+		fputs(STDERR, 'Unknow command: ' . $command . '\n');
                 exit($usage);
         }
     }