test code with EnableNetworking does not pass through header info

[César Del Solar]

Using the example in the README:

package main

import (
  "fmt"
  "io/ioutil"
  "net/http"

  "github.com/h2non/gock"
)

func main() {
  defer gock.Off()
  defer gock.DisableNetworking()

  gock.EnableNetworking()
  gock.New("http://httpbin.org").
    Get("/get").
    Reply(201).
    SetHeader("Server", "gock")

  res, err := http.Get("http://httpbin.org/get")
  if err != nil {
    fmt.Errorf("Error: %s", err)
  }

  // The response status comes from the mock
  fmt.Printf("Status: %d\n", res.StatusCode)
  // The server header comes from mock as well
  fmt.Printf("Server header: %s\n", res.Header.Get("Server"))
  // Response body is the original
  body, _ := ioutil.ReadAll(res.Body)
  fmt.Printf("Body: %s", string(body))
}

The response I get is

➜  test go run gock.go
Status: 201
Server header: gunicorn/19.9.0
Body: {
  "args": {},
  "headers": {
    "Accept-Encoding": "gzip",
    "Host": "httpbin.org",
    "User-Agent": "Go-http-client/1.1",
    "X-Amzn-Trace-Id": "Root=1-637bb59b-7debf317641b7b092a0d1887"
  },
  "origin": "64.94.4.36",
  "url": "http://httpbin.org/get"
}

Note the server header is gunicorn/19.9.0 instead of gock