validate response from wombat when pushing objects

@WesKetch maybe you can append the `res.body` in the exception message, because depending on the error the Push API returns specific messages:

> - Payload is invalid. Even sending a single object it must be passed as an array, i.e. `"orders": [{ ... }]`.
> - Push limit exceeded
> - Object limit exceeded
> - Payload is invalid. Every object in every array of the payload must have an id field.

which could help with debugging.