Doesn't update all options #8

It looks like updates do not actually update all the options for a chart.

In the updateChart method of ChartComponent, it only updates the xAxis and the background colors. Couldn't we simply replace the entire options object with the updated one?

So in the updateChart method you'd put something like this:
var helpers = Chart.helpers;
this.chart_instance.options = helpers.configMerge(this.chart_instance.options, options);

I discovered this because it throws an error when it tries to update doughnut charts, because they don't have scales.
Could we get this fixed so that it updates all the chart options?