fixing bug with nil max_concurrency
fixing bug with nil max_concurrency

iron-io/iron_worker_ruby_ng,iron-io/iron_worker_ruby_ng,iron-io/iron_worker_ruby_ng,iron-io/iron_worker_ruby_ng,iron-io/iron_worker_ruby_ng,iron-io/iron_worker_ruby_ng,iron-io/iron_worker_ruby_ng