Webpack 3 stats.json won't upload.

I am currently getting this error message:

```
Uncaught TypeError: Cannot read property '0' of undefined
at getTreeFromStats (App.js:50)
at FileReader.App.handleFileLoad
```

I think it has to do with the formatting of the `.json` file being different for Webpack 3 which I am running?

There is a similar message on the official webpack visualizer's issue page:

https://github.com/webpack/analyse/issues/30