Fix parameter validator found 2 errors from :registered_at and :regis…

[aovertus]

I, [2021-07-22_10:04:26#87320]  INFO -- : [Aws::ECS::Client 200 0.074061 0 retries] describe_task_definition(task_definition:"arn:aws:ecs:us-east-1:914746133600:task-definition/kith-staging_worker:738")
error: parameter validator found 2 errors:
  - unexpected value at params[:registered_at]
  - unexpected value at params[:registered_by]

aws/aws-sdk#38