Log Message:
Update ruby-amq-protocol to 2.0.0.

## Changes between 1.9.x and 2.0.0

2.0.0 has **breaking changes** in header encoding.

### Signed Integer Encoding in Headers

Integer values in headers are now encoded as signed 64-bit
(was unsigned 32-bit previously, unintentionally).

This is a breaking change: consuming messages with integers in headers
published with older versions of this library will break!

### Signed 16 Bit Integer Decoding

Signed 16 bit integers are now decoded correctly.

### Signed 8 Bit Integer Decoding

Signed 8 bit integers are now decoded correctly.

Contributed by Benjamin Conlan.