Errors in https://docs.rs/async-std/latest/async_std/#examples ?

I might be doing PEBCAK, but the second example in:

https://docs.rs/async-std/latest/async_std/#examples

, namely:

```
use async_std::prelude::*;

#[async_std::main]
async fn main() {
let a = async { 1u8 };
let b = async { 2u8 };
assert_eq!(a.join(b).await, (1u8, 2u8))
}
```

results for me in:

```
warning: unused import: `async_std::prelude::*`
--> src/main.rs:1:5
|
1 | use async_std::prelude::*;
| ^^^^^^^^^^^^^^^^^^^^^
|
= note: `#[warn(unused_imports)]` on by default

error[E0599]: no method named `join` found for `async` block `{async block@src/main.rs:5:13: 5:26}` in the current scope
--> src/main.rs:7:18
|
7 | assert_eq!(a.join(b).await, (1u8, 2u8))
| ^^^^ method not found in `{async block@src/main.rs:5:13: 5:26}`

For more information about this error, try `rustc --explain E0599`.
warning: `foo` (bin "foo") generated 1 warning
error: could not compile `foo` (bin "foo") due to previous error; 1 warning emitted
```

, whereas the other two examples work OOB.