Migrate from gopkg to gomod

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

@@ -0,0 +1,15 @@
+// Copyright 2018 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 (aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris || zos) && go1.9
+// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris zos
+// +build go1.9
+
+package unix
+
+import "syscall"
+
+type Signal = syscall.Signal
+type Errno = syscall.Errno
+type SysProcAttr = syscall.SysProcAttr