Time sheet portal datepicker issue

[ArnsteinB]

Hi, i've been tasked to update the datepicker popup in our Time sheet portal to display weeknumbers and start each week with monday on the calendar rows. 

  $("#datetimepicker_timesheet").datetimepicker({

            format: 'YYYY-MM-DD',

            defaultDate: new Date(scope.data.weekStartsOn),

            pickTime: false,

            calendarWeeks: true,

            weekStart: 1,

            locale: MomentUtils.getMomentLocaleFormat(g_lang),

            language: MomentUtils.getMomentLocaleFormat(g_lang)

        }).on('dp.change', function(e) {

            var dateSelected = $("#week_range_from_cal").val();

            scope.data.loading = true;

            timecardPortalService.getTimeSheetByDate(dateSelected, scope.data.userId).then(function(response) {

                if (response.data.status == 'success') {

                    var timeSheetId = response.data.data.timeSheetId;

                    if (timeSheetId != scope.data.timesheetId) {

                        $timeout(function() {

                            _loadTimesheet(timeSheetId);

                        });

                    }

                    scope.data.loading = false;

                }

            });

        }).on("dp.show", function(e) {

            positionDatePicker();

            toggleDateTimePicker(true);

            makeDatePickerAccessible();

        }).on('dp.hide', function hideListener() {

            cleanUp();

        });

        datePicker = $(".bootstrap-datetimepicker-widget.dropdown-menu");

    }

i've set the updated lines to bold. 
calendarWeeks seems to work just fine,
but weekStart does not. it will always start on sunday.
i'm wondering what causes this, and/or what to do to make it display monday first



docs i've used for the datepicker:
https://bootstrap-datepicker.readthedocs.io/en/latest/options.html#weekstart