fix syntax error

Lib/Constants.php

@@ -27,7 +27,7 @@ define('WORKERMAN_CONNECT_FAIL', 1);
 define('WORKERMAN_SEND_FAIL', 2);
 
 // Compatible with php7
-if(!class_exists('Error''))
+if(!class_exists('Error'))
 {
     class Error extends Exception
     {