utf8: fix typo in utf8_util.v (#13624)

vlib/encoding/utf8/utf8_util.v

@@ -72,7 +72,7 @@ pub fn get_uchar(s string, index int) int {
 	return res
 }
 
-// raw_index - get the raw chracter from the string by the given index value.
+// raw_index - get the raw character from the string by the given index value.
 // example: utf8.raw_index('我是V Lang', 1) => '是'
 pub fn raw_index(s string, index int) string {
 	mut r := []rune{}