[Process] made cwd argument optional

src/Symfony/Component/Process/Process.php

@@ -42,7 +42,7 @@ class Process
      *
      * @throws \RuntimeException When proc_open is not installed
      */
-    public function __construct($commandline, $cwd, array $env = array(), $stdin = null, $timeout = 60, array $options = array())
+    public function __construct($commandline, $cwd = null, array $env = array(), $stdin = null, $timeout = 60, array $options = array())
     {
         if (!function_exists('proc_open')) {
             throw new \RuntimeException('The Process class relies on proc_open, which is not available on your PHP installation.');