using real random string as nonce.

server.go

 
 func buildSignature(token string) (signature, timestamp, nonce string) {
 	timestamp = fmt.Sprintf("%d", int32(time.Now().Unix()))
-	nonce = "1461107899" //a randome string cut from previous wechat request
+	nonce = RandStringRunes(10) // "1461107899" //a randome string cut from previous wechat request
 	signature = calculateSignature(timestamp, nonce, token)
 	return
 }