Update ruby-amqp to 1.5.0.

## Changes Between 1.4.x and 1.5.0

### Only Await basic.consume-ok If nowait is false

Contributed by Rian McGuire.

### Server-Named Queue Recovery Fix

Server-named queues are now correctly recovered again.

Contributed by Jack C Hong.

## Changes Between 1.3.x and 1.4.0

### connection.blocked Support

[connection.blocked](https://www.rabbitmq.com/connection-blocked.html) notifications
are now correctly supported by the library:

``` ruby
EventMachine.run do
  connection = AMQP.connect(:host => '127.0.0.1')

  connection.on_blocked do |conn, conn_blocked|
    puts "Connection blocked, reason: #{conn_blocked.reason}"
  end

  connection.on_unblocked do |conn, _|
    puts "Connection unblocked"
  end
end
```

(taca)