Datepicker's firstDay attribute doesn't work

[chosa91]

Describe the error in 1 sentence

Datepicker's firstDay attribute doesn't work. I setted it in the $scope.firstDay and in the element firstDay="{{ firstDay }}", but it's doesn't work.

[webbiesdk]

You can see in the documentation that I just pushed how first-day is set, like this: first-day="1".
Valid inputs are 0 (for sunday) or 1 (for monday).