Update Japanese translations for new landing page (#4159)

Signed-off-by: lindwurm <lindwurm.q@gmail.com>

app/javascript/mastodon/locales/ja.json

@@ -151,7 +151,7 @@
   "report.target": "問題のユーザー",
   "search.placeholder": "検索",
   "search_results.total": "{count, number}件の結果",
-  "standalone.public_title": "A look inside...",
+  "standalone.public_title": "連合タイムライン",
   "status.cannot_reblog": "この投稿はブーストできません",
   "status.delete": "削除",
   "status.favourite": "お気に入り",