Add -version flag to show version and exit with zero

main.go

@@ -26,6 +26,7 @@ func main() {
 	appID := flag.Int64("app-id", 0, "App ID")
 	instID := flag.Int64("inst-id", 0, "Installation ID")
 	export := flag.Bool("export", false, "show token as 'export GITHUB_TOKEN=...'")
+	showVersion := flag.Bool("version", false, "show version info")
 
 	origUsage := flag.Usage
 	flag.Usage = func() {
@@ -37,6 +38,13 @@ func main() {
 
 	flag.Parse()
 
+	// See https://github.com/golang/go/issues/37533
+	// I decided to implement -version flag to return 0
+	if *showVersion {
+		flag.Usage()
+		os.Exit(0)
+	}
+
 	if *appID == 0 || *instID == 0 {
 		fmt.Fprintf(os.Stderr, "App ID and Installation ID are required.\n\n")
 		flag.Usage()