Update to ES2017 async/await

[duckontheweb]

Use babel to build from source files to take advantage of async and await functionality in new ES spec.

[wbyoung]

@duckontheweb if you want a reference point to work from, this other project I created has configuration for babel including some test setup and configuration.

[ljharb]

Since you're using the airbnb eslint config, I'd also recommend https://npmjs.com/babel-preset-airbnb which it's designed to pair with.