explicitly set http status for 304
explicitly set http status for 304

CartoDB/Windshaft-cartodb,UCL-ShippingGroup/Windshaft-cartodb,CartoDB/Windshaft-cartodb,manueltimita/Windshaft-cartodb,UCL-ShippingGroup/Windshaft-cartodb,manueltimita/Windshaft-cartodb,manueltimita/Windshaft-cartodb,CartoDB/Windshaft-cartodb,CartoDB/Windshaft-cartodb,UCL-ShippingGroup/Windshaft-cartodb