fix(StoreCredit): Add display_number method

display_number is used by many partials and templates
displaying the payment source identifier to users
or admins.

StoreCredit was missing this metho, leading to errors
if a store credit is used as payment source.

(cherry picked from commit 89aaf70)

core/app/models/spree/store_credit.rb

@@ -40,6 +40,8 @@ class Spree::StoreCredit < Spree::PaymentSource
   extend Spree::DisplayMoney
   money_methods :amount, :amount_used, :amount_authorized
 
+  alias_method :display_number, :category_name
+
   # Sets this store credit's amount to a new value,
   # parsing it as a localized number if the new value is a string.
   #

core/spec/models/spree/store_credit_spec.rb

@@ -137,6 +137,12 @@
     end
   end
 
+  describe "#display_number" do
+    it "returns the category name" do
+      expect(store_credit.display_number).to eq("Exchange")
+    end
+  end
+
   describe "#display_amount" do
     it "returns a Spree::Money instance" do
       expect(store_credit.display_amount).to be_instance_of(Spree::Money)