Added unstable_batchedUpdates as breaking change to v16 post (#10954)

* Add breaking change

ReactDOM.unstable_batchedUpdates now only takes one argument.

* Reword

* Update CHANGELOG.md

_posts/2017-09-26-react-v16.0.md

@@ -162,6 +162,7 @@ React 16 includes a number of small breaking changes. These only affect uncommon
 * `componentDidUpdate` lifecycle no longer receives `prevContext` param. (See [#8631](https://github.com/facebook/react/issues/8631))
 * Shallow renderer no longer calls `componentDidUpdate` because DOM refs are not available. This also makes it consistent with `componentDidMount` (which does not get called in previous versions either).
 * Shallow renderer does not implement `unstable_batchedUpdates` anymore.
+* `ReactDOM.unstable_batchedUpdates` now only takes one extra argument after the callback.
 
 ### Packaging