json字符串经过json.Unmarshal与json.Marshal出来字符串与最初的字符串顺序不一致问题
```
func main() {
src := `{"iss":"magic-ios-1.0.0","iat":1487000471,"jti":"4861ed10","rbd":"dbac2c5f","uri":"/auth/hello","ttu":""}`
var params interface{}
err := json.Unmarshal([]byte(src), ¶ms)
if err != nil {
fmt.Printf("%v\n", err)
return
}
p, _ := json.Marshal(params)
fmt.Printf("%v, %s\n", params, p)
}
```
问题描述：
1. json原始字符串
```
src := {"iss":"magic-ios-1.0.0","iat":1487000471,"jti":"4861ed10","rbd":"dbac2c5f","uri":"/auth
/hello","ttu":""}
```
2. 经过json.Unmarshal，再次 json.Marshal的输出结果与原始字符串不一致，如下：
```
map[iss:magic-ios-1.0.0 iat:1.487000471e+09 jti:4861ed10 rbd:dbac2c5f uri:/auth/hello ttu:], {"iat":1.487000471e+09,"iss":"magic-ios-1.0.0","jti":"4861ed10","rbd":"dbac2c5f","ttu":"","uri":"/auth/hello"}
```
有人遇到这种问题嘛？json串字段顺序变了，原始字符串md5值与一次转换后的字符串md5值就不一致了。