Codeigniter Error Common Line Number 257

A PHP Error was encountered
Severity: Notice
Message: Only variable references should be returned by reference
Filename: core/Common.php
Line Number: 257

Cara menyelesaikan Error seperti diatas :

Edit nama file: system/core/Common.php, line number: 257

yang sebelumnya

return $_config[0] =& $config; 

menjadi

$_config[0] =& $config;
return $_config[0];