SQS get queue attributes fix

Previously `SQS#get_queue_attribtues` would fail to return anything when making a request, this was due to AWS expecting to receive the attributes array as a collection of indexed query params. Eg.

```
AttributeName.1 = 'QueueArn'
AttributeName.2 = 'MessageRetentionPeriod'
```

Instead of a single key as it was previously.

Please see the AWS documentation for this endpoint http://docs.aws.amazon.com/AWSSimpleQueueService/latest/APIReference/API_GetQueueAttributes.html