Fix cart fields sharing same scope

All cart page quantity fields were displaying a single max quantity instead of a different value for each one.

app/assets/javascripts/darkswarm/directives/on_hand.js.coffee

@@ -1,6 +1,7 @@
 Darkswarm.directive "ofnOnHand", ->
   restrict: 'A'
   require: "ngModel"
+  scope: true
 
   link: (scope, elem, attr, ngModel) ->
     # In cases where this field gets its value from the HTML element rather than the model,

spec/features/consumer/shopping/cart_spec.rb

@@ -176,7 +176,7 @@ feature "full-page cart", js: true do
       end
 
       describe "with insufficient stock available" do
-        xit "prevents user from entering invalid values" do
+        it "prevents user from entering invalid values" do
           add_product_to_cart order, product_with_fee
 
           variant.update_attributes!(on_hand: 2, on_demand: false)