v2: parse builtin successfully

vlib/builtin/array.v

@@ -367,7 +367,7 @@ pub fn (b []byte) hex() string {
 	mut hex := malloc(b.len * 2 + 1)
 	mut ptr := &hex[0]
 	for i := 0; i < b.len; i++ {
-		ptr += C.sprintf(charptr(ptr), '%02x', b[i])
+		ptr += C.sprintf(ptr as charptr, '%02x', b[i])
 	}
 	return string(hex)
 }