title: Missing MessageAttributes property in SQS message receiver
body: <p>All I see is this type of data:</p>
  
  <pre><code>    {
        MessageId: 'c604c772-8468-4cd2-8f3e-9b430ed52d92',
        ReceiptHandle: 'AQEBHyPYuNqFztvy9QNOHeLQg==',
        MD5OfBody: '096c6509c8628bde267adde2b105f4e4',
        Body: 'foobar'
      }
  </code></pre>
  
  <p>when I make this call to read from the queue:</p>
  
  <pre><code>const conf = {
    QueueUrl: 'https://sqs.us-west-2.amazonaws.com/920371/logging-q',
    WaitTimeSeconds: 19,  // max is 20 (off by one errors avoided!)
    MaxNumberOfMessages: 9  // max is 10 (off by one errors avoided!)
  };
  
  sqs.receiveMessage(conf, cb);
  </code></pre>
  
  <p>but I addeded MessageAttributes when put the messages on the queue:</p>
  
  <p>sqs.sendMessageBatch({QueueUrl,Entries: v}, cb);</p>
  
  <p>Entries is an array of:</p>
  
  <pre><code>{
      Id: uuid.v4(),
      MessageBody: 'foobar',
      MessageAttributes: {
  
        logStream: {
          StringValue: LOG_STREAM,
          DataType: 'String'
        },
  
        logGroup: {
          StringValue: LOG_GROUP,
          DataType: 'String'
        }
      }
    }
  
  </code></pre>
  
  <p>anybody know why the MessageAttributes aren't showing up when I read from the queue, even they presumably are being pushed to the queue?</p>