message: [bugfix] Stepper: Hack for iOS12 page scroll
diff: import { createNamespace, isDef, addUnit } from '../utils';
  +import { getRootScrollTop } from '../utils/dom/scroll';
  +import { isIOS } from '../utils/validate/system';
  const [createComponent, bem] = createNamespace('stepper');
  @@ -153,6 +155,13 @@ export default createComponent({
  if (this.currentValue === 0) {
  event.target.value = this.currentValue;
  }
  +
  + // Hack for iOS12 page scroll
  + // https://developers.weixin.qq.com/community/develop/doc/00044ae90742f8c82fb78fcae56800
  + /* istanbul ignore next */
  + if (isIOS()) {
  + window.scrollTo(0, getRootScrollTop());
  + }
  },
  longPressStep() {
  