Add missing ? operator after handle.await
According to line#118, there should be a `?` operator after `await`.
@@ -111,7 +111,7 @@ We can "fix" it by waiting for the task to be joined, like this:
#
# async move |stream| {
let handle = task::spawn(connection_loop(stream));
-handle.await
+handle.await?
# };
```
