Fix whitespace

Author: sledgehammervampire

compiler/rustc_error_codes/src/error_codes/E0373.md

@@ -70,5 +70,5 @@ fn game_loop(v: Arc<Vec<usize>>) {}
 ```
 
 Similarly to closures, `async` blocks are not executed immediately and may
-capture closed-over data by reference. For more information, see 
-https://rust-lang.github.io/async-book/03_async_await/01_chapter.html.
+capture closed-over data by reference. For more information, see
+https://rust-lang.github.io/async-book/03_async_await/01_chapter.html.