windows build failure

```
GOOS=windows go get github.com/cloudflare/redoctober

# github.com/cloudflare/redoctober/vendor/github.com/coreos/go-systemd/activation
../go/src/github.com/cloudflare/redoctober/vendor/github.com/coreos/go-systemd/activation/files.go:57:22: cannot use fd (type int) as type syscall.Handle in argument to syscall.CloseOnExec
```
