message: fix pullUpLoad threshold bug
diff: @@ -12,7 +12,7 @@ export function pullUpMixin(BScroll) {
  this.on('scroll', checkToEnd)
  function checkToEnd() {
  - if (this.y <= (this.maxScrollY + threshold)) {
  + if (this.y <= (this.maxScrollY - threshold)) {
  this.trigger('pullingUp')
  this.off('scroll', checkToEnd)
  }
  