I suggest `default_options` use String keys. It seems qless does this [elsewhere](https://github.com/backupify/qless/blob/master/lib/qless/job.rb#L84).

Also since `default_options` seems as though it will only ever be merged w/ another Hash, you could constantize it and avoid instantiating it during every initialization. Probably not important (I think the previously referenced else where would actually benefit from constantization more)