WebRick Proxy to Github API

I'm trying to make a proxy to send every request to the github api, but I keep getting the 'hello world' message, what am I doing wrong?

require 'webrick'
require 'webrick/httpproxy'
require 'uri'

proxy =
  WEBrick::HTTPProxyServer.new ProxyURI: URI('http://api.github.com'), Port: 8080

trap 'INT'  do proxy.shutdown end
trap 'TERM' do proxy.shutdown end

proxy.mount_proc '*' do |req, res|
  method = req.request_method # POST
  path_info = req.path_info # /account 
  res.body = 'Hello, world!'
end

proxy.start

ruby / webrick

WebRick Proxy to Github API #62