crypto.rand: update slice method to slice syntax & fix typo in error

vlib/crypto/rand/rand_linux.v

@@ -34,7 +34,7 @@ pub fn read(bytes_needed int) ?[]byte {
 
 fn getrandom(bytes_needed int, buffer voidptr) int {
 	if bytes_needed > read_batch_size {
-		panic('getrandom() dont request more thane $read_batch_size bytes at once.')
+		panic('getrandom() dont request more than $read_batch_size bytes at once.')
 	}
 	return C.syscall(C.SYS_getrandom, buffer, bytes_needed, 0)
 }

vlib/crypto/rand/utils.v

@@ -43,7 +43,7 @@ fn bytes_to_u64(b []byte) []u64 {
 	mut z := [u64(0)].repeat((b.len + ws - 1) / ws)
 	mut i := b.len
 	for k := 0; i >= ws; k++ {
-		z[k] = binary.big_endian_u64(b.slice(i-ws, i))
+		z[k] = binary.big_endian_u64(b[i-ws..i])
 		i -= ws
 	}
 	if i > 0 {