message: improve:readability of updateChildren
diff: @@ -412,7 +412,7 @@ export function createPatchFunction (backend) {
  if (sameVnode(elmToMove, newStartVnode)) {
  patchVnode(elmToMove, newStartVnode, insertedVnodeQueue)
  oldCh[idxInOld] = undefined
  - canMove && nodeOps.insertBefore(parentElm, newStartVnode.elm, oldStartVnode.elm)
  + canMove && nodeOps.insertBefore(parentElm, elmToMove.elm, oldStartVnode.elm)
  newStartVnode = newCh[++newStartIdx]
  } else {
  // same key but different element. treat as new element
  