Fix lack of uniqueness

This should solve your problems with uniqueness.

```sh
➜  sidekiq-not-unique-jobs git:(master) ✗ ruby test_uniqueness.rb
2014-05-11T08:05:57Z 61376 TID-znnu9k INFO: Sidekiq client with redis options {:url=>"redis://localhost:6379", :namespace=>"sk"}
Expecting counter = 1
counter = 1
Expecting counter = 1
counter = 1
Expecting counter = 2
counter = 2
```