docs: Fix the warning "unclosed HTML tag Notifier"

Fix "unclosed HTML tag `Notifier`" warning

Signed-off-by: Tim Zhang <[email protected]>

src/asynchronous/shutdown.rs

@@ -32,7 +32,7 @@ pub struct Waiter {
 
 /// Used to Notify all [`Waiter`s](Waiter) shutdown.
 ///
-/// No `Clone` is provided. If you want multiple instances, you can use Arc<Notifier>.
+/// No `Clone` is provided. If you want multiple instances, you can use `Arc<Notifier>`.
 /// Notifier will automatically call shutdown when dropping.
 #[derive(Debug)]
 pub struct Notifier {