Fix namespaces for Zeitwerk class loader

app/models/concerns/invoice/payable.rb

@@ -1,28 +1,24 @@
-module Concerns
-  module Invoice
-    module Payable
-      extend ActiveSupport::Concern
+module Invoice::Payable
+  extend ActiveSupport::Concern
 
-      included do
-        scope :unpaid, -> { where('id NOT IN (SELECT invoice_id FROM account_activities WHERE' \
-                              ' invoice_id IS NOT NULL)') }
-      end
+  included do
+    scope :unpaid, -> { where('id NOT IN (SELECT invoice_id FROM account_activities WHERE' \
+                          ' invoice_id IS NOT NULL)') }
+  end
 
-      def payable?
-        unpaid? && not_cancelled?
-      end
+  def payable?
+    unpaid? && not_cancelled?
+  end
 
-      def paid?
-        account_activity
-      end
+  def paid?
+    account_activity
+  end
 
-      def receipt_date
-        account_activity.created_at.to_date
-      end
+  def receipt_date
+    account_activity.created_at.to_date
+  end
 
-      def unpaid?
-        !paid?
-      end
-    end
+  def unpaid?
+    !paid?
   end
 end