Fixing a little bug in php<5.5

The bin/mage script returns "Can't use function return value in write context" in php<5.5

bin/mage

@@ -8,8 +8,8 @@
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */
-
-if (empty(ini_get('date.timezone'))) {
+$timezone = ini_get('date.timezone');
+if (empty($timezone)) {
     date_default_timezone_set('UTC');
 }