How to enable the undefined middleware method when dealing with rack errors

Question

I installed Rack-bug in ruby. I added

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

to config / environment / development.rb file. when the server starts, load_environment': undefined methodmiddleware ' appears for #<Rails::Configuration:0x7f7e80b53b18> (NoMethodError). However, in the configuration the same thing is mentioned in many sites. How can I solve this problem? I am using rail-2.2.2.