message: optimize pullup load,make sure pullingup event will not trigger many times in some edge cases
diff: @@ -10,9 +10,6 @@ export function pullUpMixin(BScroll) {
  }
  BScroll.prototype._watchPullUp = function () {
  - if (this.pullupWatching) {
  - return
  - }
  this.pullupWatching = true
  const {threshold = 0} = this.options.pullUpLoad
  @@ -20,7 +17,10 @@ export function pullUpMixin(BScroll) {
  function checkToEnd(pos) {
  if (this.movingDirectionY === DIRECTION_UP && pos.y <= (this.maxScrollY + threshold)) {
  + // reset pullupWatching status after scroll end.
  + this.once('scrollEnd', () => {
  this.pullupWatching = false
  + })
  this.trigger('pullingUp')
  this.off('scroll', checkToEnd)
  }
  @@ -28,7 +28,7 @@ export function pullUpMixin(BScroll) {
  }
  BScroll.prototype.finishPullUp = function () {
  - if (this.isInTransition) {
  + if (this.pullupWatching) {
  this.once('scrollEnd', () => {
  this._watchPullUp()
  })
  