code: func (n *Negroni) Run(addr ...string) {
  	l := log.New(os.Stdout, "[negroni] ", 0)
  	finalAddr := detectAddress(addr...)
  	l.Printf("listening on %s", finalAddr)
  	l.Fatal(http.ListenAndServe(finalAddr, n))
  }
docs: // Run is a convenience function that runs the negroni stack as an HTTP
  // server. The addr string, if provided, takes the same format as http.ListenAndServe.
  // If no address is provided but the PORT environment variable is set, the PORT value is used.
  // If neither is provided, the address' value will equal the DefaultAddress constant.