QueryList query.changes.subscribe is not a function

From the CHANGELOG: 

```
Before: query.onChange(() => ...);
After: query.changes.subscribe((iterable) => {});
```

This throws `query.changes.subscribe is not a function` in alpha.40: http://plnkr.co/edit/8hcr2WIjmSuwiAV0wEmN?p=preview (see container.ts)

It works with query.changes._subject.subscribe though, so I'm not sure if it's a documentation issue or a bug :)
