Fix assets:compile

lib/tasks/assets.thor

@@ -14,7 +14,9 @@ class AssetsCLI < Thor
   option :keep, type: :numeric, default: 0, desc: 'Number of old assets to keep'
   option :verbose, type: :boolean
   def compile
+    load 'tasks/sprites.thor'
     invoke 'sprites:generate', [], :verbose => options[:verbose]
+
     manifest.compile App.assets_compile
     manifest.clean(options[:keep]) if options[:clean]
   end