Remove vendor directory and add it to the ignore list

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

@@ -1,13 +0,0 @@
-// Copyright 2015 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.
-
-// +build darwin dragonfly freebsd linux netbsd openbsd solaris
-
-package unix
-
-const (
-	R_OK = 0x4
-	W_OK = 0x2
-	X_OK = 0x1
-)