How do I make the validation rule `before:end_date` +1 day? I.E. I want to make the rule before or including the end date. I know that the date is passed to the php strtotime function which takes '+1 days' as an argument but I can't get it to work.

```
protected $fillable = array('name','start_date', 'end_date', 'registration_start', 'registration_end');

public static $rules = array(
    'registration_end' => 'required|date|before:end_date + 1 days'
);

```