Fix order_spec related to retrieving previously ordered items

In spree 2, each completed_order_with_totals comes with 5 line items (see order_factory in spree), so instead of 1+1+1=3 the calculation becomes 5+5+1=11

spec/models/spree/order_spec.rb

@@ -761,7 +761,7 @@ describe Spree::Order do
       it "returns previous items" do
         prev_order.add_variant(product.master, 1, 3)
         prev_order2.reload # to get the right response from line_items
-        expect(order.finalised_line_items.length).to eq 3
+        expect(order.finalised_line_items.length).to eq 11
         expect(order.finalised_line_items).to match_array(prev_order.line_items + prev_order2.line_items)
       end
     end