_activateOption(collection, newOption) {
      if (newOption) {
        if (!this.isMultiple) {
          collection.find('li.selected').removeClass('selected');
        }
        let option = $(newOption);
        option.addClass('selected');
      }
    }
Make option as selected and scroll to selected position
@param {jQuery} collection  Select options jQuery element
@param {Element} newOption  element of the new option