Build not working on Safari

Spread operator not being transformed breaks Safari:
![image](https://user-images.githubusercontent.com/1118293/39610687-87464590-4f28-11e8-9368-4c254754d1ff.png)

![image](https://user-images.githubusercontent.com/1118293/39610823-5a3cc28a-4f29-11e8-85ff-d76d79574684.png)

Not supported on IE11 too.
See [babel reference](https://babeljs.io/docs/plugins/transform-es2015-spread)
