fix. 语言文件缺失

Author: GregTaoo

src/main/resources/assets/concerto/lang/en_us.json

@@ -16,6 +16,7 @@
   "concerto.success": "Success",
   "concerto.fail": "Fail",
   "concerto.not_cacheable": "Not cacheable",
+  "concerto.not_available": "Concerto not available in this server!",
   "concerto.drag_confirm": "Do you want to add the following files/folders to Concerto?",
   "concerto.thank_you": "Thank you! Your support keeps me going always!",
 

src/main/resources/assets/concerto/lang/zh_cn.json

@@ -16,6 +16,7 @@
   "concerto.success": "成功",
   "concerto.fail": "失败",
   "concerto.not_cacheable": "不是可缓存的",
+  "concerto.not_available": "Concerto 在该服务器不可用！",
   "concerto.drag_confirm": "确认将下列 文件/文件夹 添加到 Concerto?",
   "concerto.thank_you": "感谢支持！您的支持是我更新的最大动力",