[Question]Why are no `async` on some resolver methods?

Hi, I'm very new to Apollo graphql and reading through the tutorial.
I noticed that `launch` method in resolver.js does not have `async` and wondering why even though the request is asynchronous. In fact, if I add async it works as expected. Could someone tell me why `async` is not required in this case?

```
module.exports = {
Query: {
launches: async (_, __, { dataSources }) =>
dataSources.launchAPI.getAllLaunches(),
launch: (_, { id }, { dataSources }) => // no async
dataSources.launchAPI.getLaunchById({ launchId: id }),
me: async (_, __, { dataSources }) =>
dataSources.userAPI.findOrCreateUser(),
},
};
```

从 resolver.js 和 issue 中展示的 Query resolver 开始，然后检查 dataSources.launchAPI.getLaunchById 以及 launches 和 me 方法。记录 launch resolver 不使用 async 编写的原因，并让面向 tutorial 读者的解释清晰易懂；当在 tutorial 上下文中回答了关于 async 的问题时，即表示完成。

由索引模型根据 Issue 内容生成。