In version 2.1.5
changeDate has been renamed to change.dp so changedate was not working for me
$("#datetimepicker").datetimepicker().on('change.dp', function (e) {
FillDate(new Date());
});
also needed to change css class from datepicker to datepicker-input
Date formate also works in capitals like this data-format='MM-DD-YYYY'
it might be helpful for someone it gave me really hard time :)