add a password parameter to the redisOpt hash so we can use heroku addons

This is a simple change so that authenticated redis URLs, like what is used in heroku addons, can be used by bull. I thought about having a factory function but decided an additional value in the hash is better.

BTW it seems that there is no documentation that a hash can be passed as the second parameter in Queue(...), I can also make that change.

I'm not sure the easiest way to add a test for this, either. Open to thoughts.