message: use next in slide
diff: this.dots = new Array(this.children.length)
  },
  _play() {
  - let pageIndex = this.currentPageIndex + 1
  clearTimeout(this.timer)
  this.timer = setTimeout(() => {
  - this.slide.goToPage(pageIndex, 0, 400)
  + this.slide.next()
  }, this.interval)
  }
  }
  