[refactor] move conditional build instance up

pkg/helper/windows_install.go

 // +build windows
+
 // Copyright 2012 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.

pkg/helper/windows_manage.go

+// +build windows
+
 // Copyright 2012 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 windows
-
 package helper
 
 import (

pkg/helper/windows_service.go

+// +build windows
+
 // Copyright 2012 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 windows
-
 package helper
 
 import (