jsonrpc/Client: 修复注解类型错误，修复客户端不传参时报错的错误

jsonrpc/Client.php

@@ -101,13 +101,13 @@ class Client
 
     /**
      * 异步调用实例
-     * @var string
+     * @var array
      */
     protected static $asyncInstances = array();
 
     /**
      * 同步调用实例
-     * @var string
+     * @var array
      */
     protected static $instances = array();
 
@@ -182,7 +182,7 @@ class Client
      * @throws Exception
      * @return 
      */
-    public function __call($method, $arguments)
+    public function __call($method, $arguments = [])
     {
         // 判断是否是异步发送
         if (0 === strpos($method, self::ASYNC_SEND_PREFIX)) {