make rubocop happy with the example on README
make rubocop happy with the example on README

lib/tasks/jobs.rake:5:29: C: [Correctable] Style/SymbolProc: Pass &:schedule as an argument to each instead of a block.
    CronJob.subclasses.each { |job| job.schedule }
                            ^^^^^^^^^^^^^^^^^^^^^^
codez/delayed_cron_job