Red favicon for dev (#2470)

* Set a dev specific favicon

* Consistent spacing

* Add trailing slash for consistency

* Update to remove interpolation

app/helpers/application_helper.rb

@@ -13,4 +13,9 @@ module ApplicationHelper
     other_classes = "#{other_classes} rtl" if [:ar, :fa].include?(I18n.locale)
     other_classes
   end
+
+  def favicon_path
+    env_suffix = Rails.env.production? ? '' : '-dev'
+    asset_path "favicon#{env_suffix}.ico"
+  end
 end