nack(tag, requeue, multiple) -> nack(tag, multiple, requeue)

The basic.nack prototype is:
```
basic.nack(delivery-tag delivery-tag, bit multiple, bit requeue)
```

(see https://github.com/ruby-amqp/amq-protocol/blob/master/lib/amq/protocol/client.rb#L2157 or the rabbitmq specs)

The current implementation swaps the two last arguments.

bunny got some mushrooms instead of carrots that day :)

---

I couldn't run the test suite, so I apologize in advance if my pull request breaks things.