remove the E_Strict warning with php > 5.1

As of php 5.1 the use of mktime() yields a warning (see http://php.net/manual/en/function.mktime.php). This simple change should fix this and is the recommended fix by the php devs.
Removing those warnings really helps to keep the server logs nice and clean ;)
Merge pull request #13 from jamasi/patch-1

remove the E_Strict warning with php > 5.1