修改例子的bug

example/forward.php

@@ -17,7 +17,7 @@ $robot = new Vbot([
 ]);
 ]);
 
 
 $robot->server->setMessageHandler(function ($message) {
 $robot->server->setMessageHandler(function ($message) {
-    if ($message->type === 'Text') {
+    if ($message instanceof Text) {
         /** @var $message Text */
         /** @var $message Text */
         $contact = contact()->getUsernameById('hanson');
         $contact = contact()->getUsernameById('hanson');
         Text::send($contact, $message);
         Text::send($contact, $message);