Spree::Product.updated_at should be modified after PATCH /api/products/{id}

[edmondchui]

In the Spree::API::ProductController#update method

@product = find_product(params[:id])
authorize! :update, @product
options = { variants_attrs: variants_params, options_attrs: option_types_params }
@product = Core::Importer::Product.new(@product, product_params, options).update
if @product.errors.empty?
  respond_with(@product.reload, :status => 200, :default_template => :show)
else
  invalid_resource!(@product)
end

The updated_at is not modified by the call Core::Importer::Product#update.

Also, the @product.reload call seems unnecessary in the respond_with line.

I think the fix includes two parts:

1. Set the updated_at to Time.now before ``update`, i.e. change

   @product = Core::Importer::Product.new(@product, product_params, options).update

   to

   @product = Core::Importer::Product.new(@product, product_params, options)
   @product.updated_at = Time.now
   @product.update
   

2. Get rid of the necessary reload, i.e. change

     respond_with(@product.reload, :status => 200, :default_template => :show)

   to

     respond_with(@product, :status => 200, :default_template => :show)
   

[JDutil]

Would you mind submitting a PR?

[edmondchui]

1. A better place to fix the issue is within Spree::Core::Importer::Product#update. We just touch the product before returning at the end of the update method. Touching the product has the benefit of calling the after_touch callbacks on Spree::Product.
2. We cannot get rid of the @product.reload call at the end of Spree::Api::ProductController#update because the reload call actually reload all updated associations.

[JDutil]

Could you submit another PR against this repo?

[nishant-cyro]

@edmondchui - This one is working fine for me in master branch.

cc: @priyank-gupta @Mafi88 @damianlegawiec