rrule to text transformation fix

My guess you use Windows platform for development that's why there is a **%#d** format used for [strftime](http://ca1.php.net/manual/en/function.strftime.php). Anyways, this test isn't passed on Linux even if I change **%#d** to **%e**. 

What was your intention, to leave a whitespace or not before 1 digit day number? Because your test clearly tells that NOT, but the code tells the OPPOSITE. 

As I don't see any benefit for leaving a whitespace and considering `$until` is a `DateTime` object as it is, I prefer to use `DateTime::format` method.