稍微修正下你的代码：

package main

import (
    "fmt"
    "flag"
    "github.com/shogo82148/androidbinary/apk"
)

func main() {
    fileName := flag.String("filename", "", "pkg filename")
    flag.Parse()

    pkg, _ := apk.OpenFile(*fileName)
    defer pkg.Close()
    res := ""

    pkgName := pkg.PackageName()
    res += pkgName
    res += " "
    verCode := pkg.VersionCode()
    verCodeStr := fmt.Sprintf("%d", verCode)
    res += verCodeStr
    res += " "
    verName := pkg.VersionName()
    res += verName
    res += " "
    appName, _ := pkg.Label(nil)
    res += appName

    fmt.Println(res)
}