add invoice number to alternative invoices

app/views/spree/admin/orders/invoice4.html.haml

@@ -43,6 +43,9 @@
       %td{ :align => "left", colspan: 2 }  
     %tr{ valign: "top" }
       %td{ :align => "left" }
+        %br
+        = "#{t :invoice_number}:"
+        = @order.invoice_number
         %br
         = t :invoice_issued_on
         = l @order.invoice_date

config/locales/en.yml

@@ -1834,7 +1834,7 @@ en:
   abn: "ABN:"
   acn: "ACN:"
   invoice_issued_on: "Invoice issued on:"
-  order_number: "Invoice number:"
+  order_number: "Order number:"
   date_of_transaction: "Date of transaction:"
 
   menu_1_title: "Shops"