Update macros.rs: fix documentation typo.

src/libstd/macros.rs

@@ -185,7 +185,7 @@ macro_rules! eprintln {
 /// builds or when debugging in release mode is significantly faster.
 ///
 /// Note that the macro is intended as a debugging tool and therefore you
-/// should avoid having uses of it in version control for longer periods.
+/// should avoid having uses of it in version control for long periods.
 /// Use cases involving debug output that should be added to version control
 /// are better served by macros such as [`debug!`] from the [`log`] crate.
 ///