concepts/integers: Fix maximum value of u8 to 255 (#1653)

Author: bashkovich

concepts/integers/about.md

@@ -9,7 +9,7 @@ Integers all have a **bit width**, which is just the number of bits making up th
 the maximum value which can be represented by that integer type.
 
 For example, one of the most common integer types is a `u8`: an unsigned, 8-bit integer. You may
-recognize this type as a single byte. This has a minimum value of 0 and a maximum value of 256.
+recognize this type as a single byte. This has a minimum value of 0 and a maximum value of 255.
 
 Rust has 12 integer primitive types, broken out by bit width and signedness: