Fix missing route in Spree::OrdersController

I'm not sure why this spec started failing. Fixes:

```
Spree::OrdersController viewing cart when an item is in the cart the page provides the right registration path
     Failure/Error: expect(subject.registration_path).to eq registration_path

     ActionController::UrlGenerationError:
       No route matches {:action=>"index", :controller=>"registration"}
     # ./spec/controllers/spree/orders_controller_spec.rb:140:in `block (5 levels) in <top (required)>'
```

app/controllers/spree/orders_controller.rb

@@ -1,6 +1,8 @@
 module Spree
   class OrdersController < Spree::StoreController
     include OrderCyclesHelper
+    include Rails.application.routes.url_helpers
+
     layout 'darkswarm'
 
     ssl_required :show