Fix images/new.js path and add simple spec to verify the page loads correctly

Testing the file upload would be a bit more complicated

app/views/spree/admin/images/new.html.haml

@@ -7,4 +7,4 @@
       %span.or= t('spree.or')
       = link_to_with_icon 'icon-remove', t('spree.actions.cancel'), admin_product_images_url(@product), id: 'cancel_link', class: 'button'
 
-= javascript_include_tag 'admin/images/new.js'
+= javascript_include_tag 'admin/spree/images/new.js'

spec/features/admin/products_spec.rb

@@ -203,6 +203,16 @@ feature '
       expect(p.reload.property('fooprop')).to be_nil
     end
 
+    scenario "loading new image page", js: true do
+      product = create(:simple_product, supplier: @supplier2)
+
+      visit spree.admin_product_images_path(product)
+      expect(page).to have_selector ".no-objects-found"
+
+      page.find('a#new_image_link').click
+      expect(page).to have_selector "#image_attachment"
+    end
+
     scenario "deleting product images", js: true do
       product = create(:simple_product, supplier: @supplier2)
       image = File.open(File.expand_path('../../../app/assets/images/logo-white.png', __dir__))