Add unique job key to the message json

[sullimander]

I am attempting to rewrite some slow workers in Go using https://github.com/jrallison/go-workers and need to be able to remove the unique job key from redis when the worker completes, but I do not have access to the key in my Go workers. It would be great if sidekiq-unique-jobs would add the key to the message so that I can accomplish this.