message: fix(transition-group): work around rollup tree shaking
  fix
diff: @@ -101,8 +101,9 @@ export default {
  children.forEach(applyTranslation)
  // force reflow to put everything in position
  - const body: any = document.body
  - const f: number = body.offsetHeight // eslint-disable-line
  + // assign to this to avoid being removed in tree-shaking
  + // $flow-disable-line
  + this._reflow = document.body.offsetHeight
  children.forEach((c: VNode) => {
  if (c.data.moved) {
  