为Goproxy配置代理设置

I'm trying to use goproxy as an alternative to fiddler on mac OSX,

I wrote the following code, and succeeded to run it:

package main

import (
"flag"
"log"
"net/http"
"gopkg.in/elazarl/goproxy.v1"
)

func main() {
    verbose := flag.Bool("v", false, "should every proxy request be logged 
to stdout")
    addr := flag.String("addr", ":8080", "proxy listen address")

    proxy := goproxy.NewProxyHttpServer()
    proxy.Verbose = *verbose
    proxy.OnResponse().DoFunc(func(resp *http.Response, ctx 
*goproxy.ProxyCtx) *http.Response {
        contentType := resp.Header.Get("Content-Type")
        if contentType == "application/javascript" || contentType == "application/x-javascript" {
        // Do something...
        }
        return resp
    })
    log.Fatal(http.ListenAndServe(*addr, proxy))
 }

According to goproxy documentation I need to configure web proxy & secure web proxy:

I have put multiple breakpoints and run the code in debug, tried to access a website but I can't get it to stop on the breakpoint..

I think I'm missing something in the proxy settings maybe.