Update CHANGELOG.md

Grammar fixes.
Added SQS::Message batch delete operation.

You can now receive and delete messages in batches.
This is much more efficient than deleting the messages
one at a time.

    messages = queue.receive_messages(max_number_of_messages: 5)

    # do something with messages ...

    # delete the batch of messages, makes 1 request
    messages.delete

    # delete messages one-at-a-time,  makes n-requests
    messages.each(&:delete)