[bug] updated hook is called but DOM is not ready (slot + v-for)

[stackia]

Vue.js version

2.1.8

Reproduction Link

http://codepen.io/jsq2627/pen/pNMNWY

Steps to reproduce

For container components with slots, if the slots are transcluded with dynamic content, in the parent's updated hook the children's DOMs are not ready.

What is Expected?

As the document said, we should expect all children's DOMs to be ready.