最新beego怎么会出现这问题啊！为什么啊？怎么解决呢

$ go run main.go # github.com/astaxie/beego/utils F:\GitHub\gopro\src\github.com\astaxie\beego\utils\mail.go:407: undefined: sync.Pool # github.com/astaxie/beego/logs F:\GitHub\gopro\src\github.com\astaxie\beego\logs\log.go:138: undefined: sync.Pool F:\GitHub\gopro\src\github.com\astaxie\beego\logs\log.go:168: undefined: sync.Pool