Changed the way the request separates body and headers

I was GETing a .csv file from a web service and strangely the response body was being chopped. I came to this conclusion after using a `var_dump($response)` that the size of `$response->body` and the size of `$response->headers` wasn't equal (or even came close) to the size of `$response->raw`. I believe that one of the uses of `explode()` or `array_pop()` would cause data loss. Now using `substr()` and it seems that the issue was resolved.