title: Shopify cart quantity drop down not updating
body: <p>I have managed to add a dropdown to the quantity field in my cart in Shopify.  This seemingly works fine - you add the product from the product page and it is the correct amount.  You click on the quantity in the cart and the dropdown appears and you can then change it if you want, however if I change it from its original chosen number to another one, then hit the update button, the cart refreshes but the quantity, and therefore the total price, does not update to the new chosen amount.  Instead it just reverts back to the first chosen amount.</p>
  
  <p>I am not very knowledgable when it comes to JavaScript so I am not sure what I am missing.  Here is the code - if you need anything else please let me know and apologies for missing it out.</p>
  
  <pre><code>    &lt;td class="quantity"&gt;{% if item.variant.title contains "Sample" %}&lt;input type="hidden" class="field" value="{{ item.quantity }}" data-id="{{ item.variant.id }}"&gt;{{ item.quantity }}
    {% else %}
    &lt;select id="updates_{{ item.variant.id }}" name="updates[]" class="drops"&gt; 
  {% for i in (2..20) %}
  &lt;option value="{{ i }}" {% if item.quantity == i %} selected{% endif %}&gt;{{ i }}&lt;/option&gt;
  {% endfor %}
  &lt;/select&gt;{% endif %}&lt;/td&gt;
  </code></pre>
  
  <p>And then here is the bit of javascript that relates to the updating:</p>
  
  <pre><code>    CartView.prototype.events = {
        'change .quantity .field': 'updateQuantity',
        'change .instructions textarea': 'saveNote',
        'click .get-rates': 'calculateShipping',
        'keydown #address_zip': 'calculateShipping'
      };
  
  CartView.prototype.updateQuantity = function(e) {
        var id, input, quantity, url;
        input = $(e.currentTarget);
        quantity = input.val();
        id = input.data('id');
        url = "/cart/change/" + id + "?quantity=" + quantity;
        return window.location = url;
      };
  </code></pre>