Add output of integer argument

Signed-off-by: Cao Weiwei <cao.weiwei30@zte.com.cn>

pkg/mflag/example/example.go

@@ -30,6 +30,7 @@ func main() {
 		fmt.Printf("s/#hidden/-string: %s\n", str)
 		fmt.Printf("b: %t\n", b)
 		fmt.Printf("-bool: %t\n", b2)
+		fmt.Printf("-integer/-number: %d\n", i)
 		fmt.Printf("s/#hidden/-string(via lookup): %s\n", flag.Lookup("s").Value.String())
 		fmt.Printf("ARGS: %v\n", flag.Args())
 	}