v2: support horizontalBar chart

Chart.js supports horizontalBar charts as of lately, see:
http://jsfiddle.net/3xts05xu/

But it's impossible to pass horizontalBar type, because type gets lowercased on this line:
https://github.com/jhudson8/react-chartjs/blob/chartjs-v2/lib/core.js#L76

What is the purpose behind .lowercase()?
Wouldn't it be better to allow to pass any type and leave it up to chart js to throw error?

[OddEssay]

I put a PR #122 that addresses this.

@OddEssay
Great work 👍

[ramimazid]

@OddEssay How do you get HorizontalBar to work in your branch? It returns undefined when I reference it.