fix qless:work rake task

[databus23]

This is a pull request for #168 and #197.
Setting up a qless worker in the current master is pretty impossible without significant knowledge of the qless code or by finding this comment from @myronmarston.
Until the planned standalone binary exists I suggest to fix the rake task so that it matches again the documentation in the README.

[myronmarston]

We decided to do away with the rake task instead. The rake task approach works well for resque because there is very little config to run a worker, so you can just pass an ENV var or two. For Qless, the worker is super flexible and configurable (supporting redis sharding, different job reservation strategies, middleware modules and more) and you're really better off writing your own task to instantiate and run the worker configured according to your needs. So in #213 I did away with the task entirely.

Closing.