vendor: convert from glide to dep

```shell
go get -u -v github.com/golang/dep
dep init
```

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

vendor/golang.org/x/sys/windows/env_windows.go

@@ -1,25 +0,0 @@
-// Copyright 2010 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.
-
-// Windows environment variables.
-
-package windows
-
-import "syscall"
-
-func Getenv(key string) (value string, found bool) {
-	return syscall.Getenv(key)
-}
-
-func Setenv(key, value string) error {
-	return syscall.Setenv(key, value)
-}
-
-func Clearenv() {
-	syscall.Clearenv()
-}
-
-func Environ() []string {
-	return syscall.Environ()
-}