How to resolve undefined method `middleware' while running rack-bug

I have set up Rack-bug in ruby. I have added

 config.middleware.use ("Rack::Bug",
:secret_key => "epT5uCIchlsHCeR9dloOeAPG66PtHd9K8l0q9avitiaA/KUrY7DE52hD4yWY+8z1",
:password   => "some_pass"
)

into my c开发者_运维知识库onfig/environments/development.rb file. when i start server then load_environment': undefined methodmiddleware' for #<Rails::Configuration:0x7f7e80b53b18> (NoMethodError) is showing. However in configuration same thing is mentioned in many sites. How can I resolve this problem? I am using rail-2.2.2.