Update index.md

Author: Soupstraw

message-index/messages/GHC-21231/index.md

@@ -5,5 +5,5 @@ introduced: 9.6.1
 severity: error
 ---
 
-The escape sequence in the `Char` literal is too large of a number. The maximum value of a numeric literal is \1114111 
-(or \x10ffff in hexadecimal and \o4177777 in octal).
+The escape sequence in the `Char` literal is too large of a number. The maximum value of a numeric literal is `\1114111`
+(or `\x10ffff` in hexadecimal and `\o4177777` in octal).