Uses new computed property syntax w/ polyfill for host apps running older ember

[jayphelps]

http://emberjs.com/deprecations/v1.x/#toc_computed-properties-with-a-shared-getter-and-setter

[jayphelps]

There seems to be an issue with the dummy app, investigating. Don't merge yet.

[jayphelps]

OK fixed. Issue was caused by scale setter not defaulting if the cast value was NaN. https://github.com/Netflix/ember-nf-graph/pull/63/files#diff-a41a06eff671679579fa51f5381ad41eR99

 scaleOffsetY: computed({
   get() {
     return this._scaleOffsetY || 0;
   },
   set(key, value) {
     return this._scaleOffsetY = +value || 0;
   }
 })

I actually don't think storing the value in a private _scaleOffsetY, etc is necessary? It just adds to the confusion of "when is ember memoizing" vs. "when is the getter actually being called". In this case, it was memoized as NaN.

[jayphelps]

@Blesh I'm gonna go ahead and merge tonight if I don't hear otherwise from you 😋

[benlesh]

Sorry... this was a big PR, I started looking at it, but got pulled into something else.

[jayphelps]

🎉 Thanks dudebro.