bunyan日志框架自带字段重写问题

const utils = require('./utils.js');		// 时间格式化函数
const bunyan = require("bunyan");
const log = bunyan.createLogger({
    name: 'app',
    streams: [
        {
            level: 'error',
            stream:new MyRawStream(),
            type:'raw'
        }
        
    ]
});
function MyRawStream() {}
MyRawStream.prototype.write=function (rec) {
    rec.time = utils.formatTime(new Date(rec.time), 'yyyy-MM-dd hh:mm:ss');
    rec.level = bunyan.nameFromLevel[rec.level];
    console.error(JSON.stringify(rec));
}