close(index) {
      let $collapsibleLi = this.$el.children('li').eq(index);
      if ($collapsibleLi.length && $collapsibleLi[0].classList.contains('active')) {
        // onCloseStart callback
        if (typeof this.options.onCloseStart === 'function') {
          this.options.onCloseStart.call(this, $collapsibleLi[0]);
        }

        // Animate out
        $collapsibleLi[0].classList.remove('active');
        this._animateOut(index);
      }
    }
Close Collapsible
@param {Number} index - 0th index of slide