Add translation japanese "No attachments yet."

apps/app/public/static/locales/ja_JP/translation.json

@@ -57,7 +57,7 @@
   "Timeline View": "タイムライン",
   "History": "更新履歴",
   "attachment_data": "添付データ",
-  "No_attachments_yet": "No attachments yet.",
+  "No_attachments_yet": "添付データはありません",
   "Presentation Mode": "プレゼンテーション",
   "Not available for guest": "ゲストユーザーは利用できません",
   "Not available in this version": "このバージョンでは利用できません",