I found two JSON errors being shadowed; the one in amazon/validator.go
is being hidden by errors.New(responseError.Message) -- which should be
an empty string if there's a JSON error. So, it wouldn't report success,
but this gives the caller better information on what failed.
The second is in appstore/validator.go, which was ignoring encode errors
before POSTing a verify request.
Make a new method called parseResponse which essentially allows us to feed it our own response so that we can feed it bad body so that it cannot unmarshal or even read it.
Use a new struct called `HttpStatusResponse` to check the status code returned in the receipt. This is ios-type independent and will redirect the receipt to sandbox if needed.
Following Apple's recommendation, always hit production and then sandbox. There is no more need to specify which environment to hit.
In the gorequest Send method, there is a switch that checks the type of the parameter (https://github.com/parnurzeal/gorequest/blob/master/main.go#L341). In this particular case, the type of *IAPRequest is "ptr" which results in gorequest's switch to go the default case which is empty. The request was made with an empty body.
