Use proper signals for stopping sidekiq in example.

According to the sidekiqctl and documentation
https://github.com/mperham/sidekiq/blob/master/bin/sidekiqctl#L56-L79
Removed unnecessary code from start_command in sidekiq example.

sidekiq bin already have #!/usr/bin/env ruby header, so it can be
omitted
https://github.com/mperham/sidekiq/blob/master/bin/sidekiq#L1