all: replace []byte with []u8

vlib/builtin/js/int.js.v

@@ -142,7 +142,7 @@ pub fn (x byte) hex() string {
 
 // hex returns a string with the hexadecimal representation
 // of the byte elements of the array.
-pub fn (b []byte) hex() string {
+pub fn (b []u8) hex() string {
 	mut hex := ''
 	for i in b {
 		mut z := i