runtime: fix typo in `shutdown_background` docs
@@ -576,7 +576,7 @@ cfg_rt! {
/// may result in a resource leak (in that any blocking tasks are still running until they
/// return.
///
- /// This function is equivalent to calling `shutdown_timeout(Duration::of_nanos(0))`.
+ /// This function is equivalent to calling `shutdown_timeout(Duration::from_nanos(0))`.
///
/// ```
/// use tokio::runtime::Runtime;
