Wrong layout applied for absolute positioned layers with zIndex
Hi 👋

I've recently discovered that there is the wrong yoga layout applied to layers with a a `zIndex` and position set to `absolute`.

I was able to track that behavior down to the `reactTreeToFlexTree` function in `buildTree.js` so I've created a quick test to double check. You can find the PR over here: https://github.com/airbnb/react-sketchapp/pull/244

The issue is that the layers are getting correctly reordered related to their `zIndex`, but the layout got applied in the original order. It seems to be related to a typo when fetching the layer style declarations. Can you please confirm @larsonjj by looking at the PR that I've created? 

The test case I've implemented contains three layers with a zIndex set and a specific width and height. For simplicities sake the width/height is 100 times the zIndex. So the simplified setup of layers looks like this.

```
{
      type: 'view',
      props: {
        name: 'Layer 1',
        style: {
          height: 100,
          position: 'absolute',
          width: 100,
          zIndex: 1,
        },
      },
    },
    {
      type: 'view',
      props: {
        name: 'Layer 2',
        style: {
          height: 200,
          position: 'absolute',
          width: 200,
          zIndex: 2,
        },
      },
    },
    {
      type: 'view',
      props: {
        name: 'Layer 3',
        style: {
          height: 300,
          position: 'absolute',
          width: 300,
          zIndex: 3,
        },
      },
    }
```

after calculating the yoga layout and running `reactTreeToFlexTree` I expect the layout property for each of those layers to match the layout (width/height) defined by the styles. 

The current behavior applies the `layout` of Layer 1 to Layer 3 and vice versa. 
Expected bahavior is that the `layout` is applied in the same order as the layers are reordered. (Like my test case is defined). 