Fixed #67 Support iOS apns-topic flag.

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

gorush.go

@@ -27,6 +27,7 @@ func main() {
 	android := flag.Bool("android", false, "send android notification")
 	ios := flag.Bool("ios", false, "send ios notification")
 	production := flag.Bool("production", false, "production mode in iOS")
+	topic := flag.String("topic", "", "apns topic in iOS")
 
 	flag.Parse()
 
@@ -104,6 +105,10 @@ func main() {
 			Message:  *message,
 		}
 
+		if *topic != "" {
+			req.Topic = *topic
+		}
+
 		err := gorush.CheckMessage(req)
 
 		if err != nil {