Copy paste the below lines into wp_config.php file:
define(‘WP_PROXY_HOST’, ‘proxy.url.com’);
define(‘WP_PROXY_PORT’, ‘1234’);
define(‘WP_PROXY_USERNAME’, ”);
define(‘WP_PROXY_PASSWORD’, ”);
define(‘WP_PROXY_BYPASS_HOSTS’, ‘localhost’);
and change the define(‘WP_DEBUG’, TRUE);
It works.