vendor: Bump golang.org/x/sys/unix to a newer version

The current vendor of sys/unix is really old, and doesn't work on arm64 and ppc64le
Updating to the latest version might also fix other issues

ref #209

vendor/golang.org/x/sys/unix/str.go

@@ -8,8 +8,12 @@ package unix
 
 func itoa(val int) string { // do it here rather than with fmt to avoid dependency
 	if val < 0 {
-		return "-" + itoa(-val)
+		return "-" + uitoa(uint(-val))
 	}
+	return uitoa(uint(val))
+}
+
+func uitoa(val uint) string {
 	var buf [32]byte // big enough for int64
 	i := len(buf) - 1
 	for val >= 10 {