Updating Wake example to use new 'pin!' macro

Author: madsravn

library/alloc/src/task.rs

@@ -39,6 +39,7 @@ use crate::sync::Arc;
 /// use std::sync::Arc;
 /// use std::task::{Context, Poll, Wake};
 /// use std::thread::{self, Thread};
+/// use core::pin::pin;
 ///
 /// /// A waker that wakes up the current thread when called.
 /// struct ThreadWaker(Thread);
@@ -52,7 +53,7 @@ use crate::sync::Arc;
 /// /// Run a future to completion on the current thread.
 /// fn block_on<T>(fut: impl Future<Output = T>) -> T {
 ///     // Pin the future so it can be polled.
-///     let mut fut = Box::pin(fut);
+///     let mut fut = pin!(fut);
 ///
 ///     // Create a new context to be passed to the future.
 ///     let t = thread::current();