Update defaults for Cap 2

When using Capistrano 2, sidekiq.yml is not recognized by default. I've tried using this gem on two different servers and Sidekiq didn't pick up sidekiq.yml on either. 

In addition, the Capistrano 2 tasks didn't have the sidekiq_config option that the Capistrano 3 tasks have.

This is an update to correct this.