据说node7.0已经支持async/await，那么下面的代码为什么运行不了？
var sleep=function(time){
return new Promise(function(resolve,reject){
setTimeout(function(){
resolve('ok');
},time);
});
};
async function start(){
let result =await sleep(3000);
console.log(result);
}
start();
![[Web front-end] Démarrage rapide de Node.js](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
https://nodejs.org/en/docs/es6/