Fix lettuce_share_report_spec by adapting count_on_hand setter, it's not a db column anymore

spec/lib/open_food_network/lettuce_share_report_spec.rb

@@ -50,7 +50,7 @@ module OpenFoodNetwork
         end
 
         it "only available items" do
-          variant.update_column(:count_on_hand, 0)
+          variant.count_on_hand = 0
           report.stub(:child_variants) { Spree::Variant.where(id: [variant, variant2, variant3, variant4]) }
           report.send(:table).count.should eq 3
         end