Update ruby-amq-protocolto 2.1.0.

## Changes between 2.0.0 and 2.1.0

### Ruby Warnings Squashed

Contributed by Akira Matsuda.

GitHub issue: [#62](https://github.com/ruby-amqp/amq-protocol/pull/62)

### Byte Array Decoding

Byte array values in types now can be
decoded (to the extent Ruby type system
permits) by this library.

GitHub issue: [#58](https://github.com/ruby-amqp/amq-protocol/issues/58)

(taca)