Use JSON.generate on SidekiqScheduler::Schedule.set_schedule
Use JSON.generate on SidekiqScheduler::Schedule.set_schedule

yajl gem doesn't generates/parses accordingly the type of the received argument 
when invoking `Kernel#JSON` method, it just tries to parse the value. 

In order to fix that, we explcitly invoke JSON.generate
Moove-it/sidekiq-scheduler,Moove-it/sidekiq-scheduler