Update SNS error response

An example error response might look like

  <ErrorResponse xmlns="http://sns.amazonaws.com/doc/2010-03-31/">
    <Error>
      <Type>Sender</Type>
      <Code>EndpointDisabled</Code>
      <Message>Endpoint is disabled</Message>
    </Error>
    <RequestId>ad87ee7a-0d54-54c9-a450-a4bf15686747</RequestId>
  </ErrorResponse>
Merge pull request #1 from hongrich/master

Update SNS error response