`.output()` should "recurse" on any component nodes

[Mx Corey Frang]

Until it meets a depth that wasn't rendered. I.E.

const Second = () => <div>second</div>;
const First = () => <Second>first</Second>;
expect(deep(<First />).output()).toEqual(<div>second</div>);
expect(shallow(<First />).output()).toEqual(<Second>first</Second>);