gmail example gives credentials error method not found in `impl std::future::Future`

I am using the example on github here for gmail.
I get the error:
```

credentials(creds)
^^^^^^^^^^^ method not found in `impl std::future::Future`

```
I am new to rust sorry.
I tried `#[async_std::main]` but it says i should use it only on main.
What could i do?