修复str_replace($key, '', $path, 1);执行错误的bug

config/config.sample.php

@@ -92,6 +92,7 @@ return array(
                 'host'	=>	'http://127.0.0.1:9091/transmission/rpc',		// 警告！注意：transmission/rpc这段别动，你只需要修改 127.0.0.1:9091
                 'username'	=>	'',
                 'password'	=>	'',
+                'downloadDir'=> '',
             ),
         ),
         'workingMode'	=> 1,