async keyword is removed

[REPL](https://svelte.technology/repl?version=1.41.1&gist=7710173c36cc27e97038ee10a4fe62ab). The `async` keyword is removed from the `oncreate` function:

```js
export default {
  async oncreate() {
    const data = await fetch('foo.json').then(r => r.json());
    console.log(data);
  }
};
```