Change ScrollList#zoomTo Method Signature

Change ScrollList#zoomTo method signature to accept and single
arg of options, to align it with other methods.

Unit Tests
-------------

- Updated to reflect API changes

How To +10/QA
-------------

```bash
# skip the following steps if you've already initialized the project
$ git clone git@github.com:WebFilings/wf-js-uicomponents.git
$ cd wf-js-uicomponents

# do not skip these!
$ git fetch && 
git checkout change_zoom_method_signature && 
./init.sh && 
grunt qa
```

- Should see no console errors.
- Open ScrollList demo.
- Should be able to enter a different zoom level and have the scroll list update accordingly.

@lancefisher-wf 
@robbecker-wf 
@patkujawa-wf