localhost:3000我在 rails 服务器（
Error starting application
Your Rack app raised an exception when Pow tried to run it.
LoadError: cannot load such file -- rack/jsonp
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
~/config.ru:2:in `block in '
~/Library/Application Support/Pow/Versions/0.4.1/node_modules/nack/lib/nack/builder.rb:4:in `instance_eval'
~/Library/Application Support/Pow/Versions/0.4.1/node_modules/nack/lib/nack/builder.rb:4:in `initialize'
有任何想法吗？