Fix code comment

index.js

@@ -6,7 +6,7 @@ module.exports = string => {
 	}
 
 	// Escape characters with special meaning either inside or outside character sets.
-	// Use a simple backslash escape when it’s always valid, and a \unnnn escape when the simpler form would be disallowed by Unicode patterns’ stricter grammar.
+	// Use a simple backslash escape when it’s always valid, and a `\xnn` escape when the simpler form would be disallowed by Unicode patterns’ stricter grammar.
 	return string
 		.replace(/[|\\{}()[\]^$+*?.]/g, '\\$&')
 		.replace(/-/g, '\\x2d');