- Fix error string raised from `enqueue_at`

activejob/lib/active_job/queue_adapters/queue_classic_adapter.rb

@@ -26,7 +26,7 @@ def enqueue_at(job, timestamp) #:nodoc:
           queue = build_queue(job.queue_name)
           unless queue.respond_to?(:enqueue_at)
             raise NotImplementedError, 'To be able to schedule jobs with queue_classic ' \
-              'the QC::Queue needs to respond to `enqueue_at(timestamp, method, *args)`. '
+              'the QC::Queue needs to respond to `enqueue_at(timestamp, method, *args)`. ' \
               'You can implement this yourself or you can use the queue_classic-later gem.'
           end
           queue.enqueue_at(timestamp, "#{JobWrapper.name}.perform", job.serialize)