Update spec after adding default pages

The spec was assuming there was only 1 custom page created in the
DB. With this change the spec will pass no matter how many  custom
pages there are in the DB.

spec/features/admin/widgets/cards_spec.rb

@@ -147,7 +147,11 @@ feature "Cards" do
 
       scenario "Create", :js do
         visit admin_site_customization_pages_path
+
+        within "#site_customization_page_#{custom_page.id}" do
           click_link "See Cards"
+        end
+
         click_link "Create card"
 
         fill_in "Title", with: "Card for a custom page"