Merge pull request #348 from arassypnov/patch-1

If the reply_markup isn't a Keyboard object, this fixes it!

Thanks @arassypnov

src/Request.php

@@ -204,7 +204,7 @@ public static function execute($action, array $data = [])
     {
         //Fix so that the keyboard markup is a string, not an object
         if (isset($data['reply_markup'])) {
-            $data['reply_markup'] = (string)$data['reply_markup'];
+            $data['reply_markup'] = json_encode($data['reply_markup']);
         }
 
         $request_params = self::setUpRequestParams($data);