code固定为-32000

https://github.com/hyperf/json-rpc/blob/522188e41fae8489940416de839866b85ce029d5/src/CoreMiddleware.php#L52

可以这个位置修改成统一的格式吗,而且code固定为SERVER_ERROR了,可以交给用户抛出的code吗,在异常app\Exception\Handler\里面也无法修改响应格式

```json
{
"code": -32000,
"message": "No query results for model xx.",
"data": {
"class": "Hyperf\\Database\\Model\\ModelNotFoundException",
"code": 0,
"message": "No query results for model xx."
}
}

{
"code": 200,
"data": {
"no": "12345678"
},
"message": ""
}
```