test: Update doc tests for bit_width

Author: sorairolake

library/core/src/num/uint_macros.rs

@@ -224,8 +224,9 @@ macro_rules! uint_impl {
         /// ```
         /// #![feature(uint_bit_width)]
         ///
-        #[doc = concat!("assert_eq!(0", stringify!($SelfT), ".bit_width(), 0);")]
-        #[doc = concat!("assert_eq!(7", stringify!($SelfT), ".bit_width(), 3);")]
+        #[doc = concat!("assert_eq!(0_", stringify!($SelfT), ".bit_width(), 0);")]
+        #[doc = concat!("assert_eq!(0b111_", stringify!($SelfT), ".bit_width(), 3);")]
+        #[doc = concat!("assert_eq!(0b1110_", stringify!($SelfT), ".bit_width(), 4);")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.bit_width(), ", stringify!($BITS), ");")]
         /// ```
         #[unstable(feature = "uint_bit_width", issue = "142326")]