Add support for calculate and dynamically change offset position for …

Created by: romanlex

Sorry for bad English. Add support for calculate and dynamically change offset position for dropdown menu. Function call always when call Popper.js modifierFn. Now I can change dynamically position of dropdown menu

            $('[data-toggle="dropdown"]').dropdown({
                offsetFn: function(data) {
                    data.left = -100;
                    return data
                }
            });