In [ok](https://github.com/websdk/nap/blob/master/src/nap.js#L51) responses, we add a body; but in [error](https://github.com/websdk/nap/blob/master/src/nap.js#L59) responses, we don't. We should change that.
In ok responses, we add a body; but in error responses, we don't. We should change that.