Fix missing vendor dir

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

@@ -0,0 +1,11 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build ios
+
+package unix
+
+func ptrace(request int, pid int, addr uintptr, data uintptr) (err error) {
+	return ENOTSUP
+}