upg.Exit() do not effective in go routine ?

```
go func(upg *tableflip.Upgrader) {
for {
select {
case <-upg.Exit():
fmt.Println("Exit111111111111111111111111111")
break
}
}
}(upg)
```

in this case , `upg.Exit()` not triggered ?

### complete example

```
package main

import (
"fmt"
"log"
"net/http"
"os"
"os/signal"
"syscall"
"time"

"github.com/cloudflare/tableflip"
)

// 當前程序的版本
const version = "v0.0.1"

func main() {
upg, err := tableflip.New(tableflip.Options{})
if err != nil {
panic(err)
}
defer upg.Stop()

// 爲了演示方便，爲程序啓動強行加入 1s 的延時，並在日誌中附上進程 pid
time.Sleep(time.Second)
log.SetPrefix(fmt.Sprintf("[PID: %d] ", os.Getpid()))

// 監聽系統的 SIGHUP 信號，以此信號觸發進程重啓
go func() {
sig := make(chan os.Signal, 1)
signal.Notify(sig, syscall.SIGHUP)
for range sig {
// 核心的 Upgrade 調用
err := upg.Upgrade()
if err != nil {
log.Println("Upgrade failed:", err)
}
}
}()

// 注意必須使用 upg.Listen 對端口進行監聽
ln, err := upg.Listen("tcp", ":8080")
if err != nil {
log.Fatalln("Can't listen:", err)
}

// 創建一個簡單的 http server，/version 返回當前的程序版本
mux := http.NewServeMux()
mux.HandleFunc("/version", func(rw http.ResponseWriter, r *http.Request) {
log.Println(version)
rw.Write([]byte(version + "\n"))
})
server := http.Server{
Handler: mux,
}

// 照常啓動 http server
go func() {
err := server.Serve(ln)
if err != http.ErrServerClosed {
log.Println("HTTP server:", err)
}
}()

if err := upg.Ready(); err != nil {
panic(err)
}

go func(upg *tableflip.Upgrader) {
for {
select {
case <-upg.Exit():
fmt.Println("Exit111111111111111111111111111")
break
}
}
}(upg)

time.Sleep(10 * time.Hour)

//<-upg.Exit()

}

```