Continuation should be eager_autoload

Otherwise it will only be loaded when the first job that uses Continuable
is enqueued or executed.

Author: rafaelfranca

activejob/lib/active_job.rb

@@ -41,9 +41,9 @@ module ActiveJob
   autoload :SerializationError, "active_job/arguments"
   autoload :UnknownJobClassError, "active_job/core"
   autoload :EnqueueAfterTransactionCommit
-  autoload :Continuation
 
   eager_autoload do
+    autoload :Continuation
     autoload :Serializers
     autoload :ConfiguredJob
   end