Do not assign order_id on inventory units in specs

order_id column has been removed from solidus since solidusio/solidus#2377.
Now the order reference will be taken from the shipment in which the
inventory units are included.

lib/solidus_expedited_exchanges/unreturned_item_charger.rb

@@ -62,7 +62,7 @@ def add_exchange_variants_to_order
       @return_items.group_by(&:exchange_variant).map do |variant, variant_return_items|
         variant_inventory_units = variant_return_items.map(&:exchange_inventory_unit)
         line_item = Spree::LineItem.create!(variant: variant, quantity: variant_return_items.count, order: new_order)
-        variant_inventory_units.each { |i| i.update_attributes!(line_item_id: line_item.id, order_id: new_order.id) }
+        variant_inventory_units.each { |i| i.update_attributes!(line_item_id: line_item.id) }
       end
     end
 

lib/tasks/exchanges.rake

@@ -9,7 +9,7 @@ namespace :exchanges do
 
     # Determine that a return item has already been deemed unreturned and therefore charged
     # by the fact that its exchange inventory unit has popped off to a different order
-    unreturned_return_items.select! { |ri| ri.inventory_unit.order_id == ri.exchange_inventory_unit.order_id }
+    unreturned_return_items.select! { |ri| ri.inventory_unit.order.id == ri.exchange_inventory_unit.order.id }
 
     failures = []