Update order spec to test an order with a total > 0

This is necessary because the previous commit changed the logic
around payment state, meaning that a complete order with a total
of 0 and no complete paymnents is considered to have a payment
state of 'paid'. I don't think this is problematic, since it is
not possible to check out an order without line items.

This way the spec tests an order modelled on the real world.

spec/models/spree/order_spec.rb

@@ -181,7 +181,7 @@ describe Spree::Order do
   end
 
   describe "an unpaid order with a shipment" do
-    let(:order)           { create(:order, shipping_method: shipping_method) }
+    let(:order)           { create(:order_with_totals, shipping_method: shipping_method) }
     let(:shipping_method) { create(:shipping_method) }
 
     before do