response stream not correct

nodejs:
```js
const express = require("express");
const app = express();

app.get('/', function (req, res) {
res.write('hello\n');
setTimeout(() => {
res.write('world');
res.end();
}, 5000);
});
app.listen(3000);
```
When `curl http://localhost:3000`, it will show `hello` first, then wait 5 seconds show `world`.

But it shows `hello world` in 5 seconds together in Deno.
```js
import express from "npm:express@4.18.2";
const app = express();
app.get("/", (req, res) => {
res.write("hello\n");
setTimeout(() => {
res.write("world");
res.end();
}, 5000);
});

app.listen(3000);
```