Ctrl-C to umount

[wade-fs]

I met the Ctrl-C to zipfs will cause manual umount.
Please add the following after mountpoint := flag.Arg(1)

cc := make(chan os.Signal, 1)
signal.Notify(cc, os.Interrupt)
go func(){
    for range cc {
        fuse.Unmount(mountpoint)
    }
}()