Update src/libcore/num/mod.rs

Co-authored-by: lzutao <taolzu@gmail.com>

Author: Amanieu

src/libcore/num/mod.rs

@@ -3309,8 +3309,8 @@ Basic usage:
 
 ```
 ", $Feature, "assert_eq!(100", stringify!($SelfT), ".saturating_add(1), 101);
-assert_eq!((", stringify!($SelfT), "::MAX).saturating_add(127), ", stringify!($SelfT),
-"::MAX);", $EndFeature, "
+assert_eq!(", stringify!($SelfT), "::MAX.saturating_add(127), ", stringify!($SelfT), "::MAX);",
+$EndFeature, "
 ```"),
 
             #[stable(feature = "rust1", since = "1.0.0")]