Close bug

[BoxuanXu]

hello，here is a bug,if err is not nil, then defer res.Body.Close(),will panic.
`func (request *Request) Execute() (response string, ret error) {
if request.ApiKey == "" || request.Method == "" {
return "", Error("Need both API key and method")
}

s := request.URL()

res, err := http.Get(s)
defer res.Body.Close()
if err != nil {
	return "", err
}

body, _ := ioutil.ReadAll(res.Body)
return string(body), nil

}`