message: chore(example): update scroll example
diff: <script type="text/ecmascript-6">
  import BScroll from '../../../src/index'
  + import PullDown from '../../../src/plugins/pull-down/pull-down'
  + import PullUp from '../../../src/plugins/pull-up/pull-up'
  import Loading from '../loading/loading.vue'
  import Bubble from '../bubble/bubble.vue'
  import { getRect } from '../../common/js/dom'
  + BScroll.use(PullDown)
  + BScroll.use(PullUp)
  +
  const COMPONENT_NAME = 'scroll'
  const DIRECTION_H = 'horizontal'
  const DIRECTION_V = 'vertical'
  