Make kewatcher accept redis authorization

[max-reznichenko]

Current implementation doesn't accept redis authorization. Basically if I provide password, it just get omitted.

Ref: https://github.com/kmullin/resque-sliders/blob/master/lib/resque-sliders/kewatcher.rb#L43

[kmullin]

Yep, you're right. Somewhat embarrassing really.

If you'd like this functionality, you could open a pull request.