Bug: SNS Confirmation JSON POST request sent as text/plain

SNS confirmation emails are sent out with a JSON body but the content-type is 'text/plain' where it should be application/json so the body can be parsed by built-in parsers.

Eg. in Python Flask if you try to use request.get_json() on the confirmation request it returns a 400 Bad Request as Flask won't parse the body if the content-type is wrong.

Please fix!