go语言调用阿里云OpenApi的签名加密问题？

https://help.aliyun.com/document_detail/25492.html?spm=5176.doc25490.2.2.Uwn9UA

我按照url的文档，对StringToSign进行hmac sha1进行加密，然后base64，得到的结果与文档例子的结果不一致 v2-c7765a6260196517ed843e4f01d9e381_r.png

我的代码：

package main

import "fmt"

import "crypto/sha1"

import "crypto/hmac"

import b64 "encoding/base64"

func main() {

    key := []byte("testsecret&")
    mac := hmac.New(sha1.New, key)
    mac.Write([]byte("GET&%2F&AccessKeyId%3Dtestid&Action%3DDescribeRegions&Format%3DXML&SignatureMethod%3DHMAC-SHA1&SignatureNonce%3D3ee8c1b8-83d3-44af-a94f-4e0ad82fd6cf&SignatureVersion%3D1.0&TimeStamp%3D2016-02-23T12%253A46%253A24Z&Version%3D2014-05-26"))
    s := b64.StdEncoding.EncodeToString(mac.Sum(nil))
    fmt.Println(s)
}

输出的结果：LZ5DVzNj95387UDL70u7+18AwWY= 与官网文档结果不一致，搞了一天了，不知道啥原因!