Update UploadManager.php

兼容直接调用put方法未指定fname时上传响应400的问题

Author: ankadada

src/Qiniu/Storage/UploadManager.php

@@ -46,7 +46,7 @@ public function put(
         $data,
         $params = null,
         $mime = 'application/octet-stream',
-        $fname = null
+        $fname = "default_filename"
     ) {
 
         $params = self::trimParams($params);