google-analytics-chart 'data' property does not notify

[zinkkrysty]

This means we cannot bind to changes in the data property if we want to re-use it for something else (extra data processing for example). It defeats the purpose to have the property in the public API if we cannot use it in this way.

To solve this, one has to add notify: true here. I can make a pull request for this if you think it is a good idea.

[ebidel]

Yea that makes sense to me. PR would be great!