I started using a switch, because you were handling more response codes like 422 explicitly. Now those errors are all automatically detected converted to a `BraintreeError` object. I had multiple cases in there before like `422` and `404`, but removed them in favor of simplicitly.

Of course now the switch seems kind of obsolete, but I left them in in case there might be more `2xx` codes (I don't really know, don't have a complete overview of all response codes that BT might return)