updated app_middleware call to use string version as to make sure constant is loaded
updated app_middleware call to use string version as to make sure constant is loaded

CarlosCD/airbrake,nick-desteffen/airbrake,kakra/hoptoad_notifier,thoughtbot/hoptoad_notifier,airbrake/airbrake,Shopify/airbrake,nick-desteffen/airbrake,square/hoptoad_notifier,stevecrozz/hydraulic_brake,CarlosCD/airbrake,airbrake/airbrake,thoughtbot/airbrake,benjaminoakes/airbrake