We've made a fork with the fixes with detail documentation:
Forked Repository:
Usage:
jQuery(document).ready(function($) {
    if (window.jQuery().datetimepicker) {
        $('.datetimepicker').datetimepicker({
            // Formats
            // follow MomentJS docs: https://momentjs.com/docs/#/displaying/format/
            format: 'DD-MM-YYYY hh:mm A',
            // Your Icons
            // as Bootstrap 4 is not using Glyphicons anymore
            icons: {
                time: 'fa fa-clock-o',
                date: 'fa fa-calendar',
                up: 'fa fa-chevron-up',
                down: 'fa fa-chevron-down',
                previous: 'fa fa-chevron-left',
                next: 'fa fa-chevron-right',
                today: 'fa fa-check',
                clear: 'fa fa-trash',
                close: 'fa fa-times'
            }
        });
    }
});
Credits:
Thanks to Eonasdan for the awesome library. Thanks to 非良 (wgbbiao) for their fork too. Thanks to Camille Anelli's blog for the reminder about the icons.