Fix app generator so that it uses the right app_name during rails:upd…

…ate rake task. [#5207 state:committed]

Signed-off-by: José Valim <jose.valim@gmail.com>

railties/lib/rails/tasks/framework.rake

@@ -54,7 +54,7 @@ namespace :rails do
 
   namespace :update do
     def invoke_from_app_generator(method)
-      app_generator.invoke(method)
+      app_generator.send(method)
     end
 
     def app_generator