Update announcements.json

announcements.json

 [
-    {"id":24,"title":"数据端更新中，所有服务暂时停止。","url":"http://fff.ac/nzl3eu","created_at":"2015-05-07T21:20:06+08:00","updated_at":"2015-05-17T21:20:06+08:00"},
     {"id":24,"title":"v1.5.1 更新CORE|VJMP|VS15|YZ08新卡（96张）","url":"http://fff.ac/grrfbs","created_at":"2015-05-07T21:20:06+08:00","updated_at":"2015-05-17T21:20:06+08:00"},
     {"id":24,"title":"v1.5.0 更新CROS新卡（89张）","url":"http://fff.ac/tizaz2","created_at":"2015-02-28T19:34:06+08:00","updated_at":"2015-03-08T19:34:06+08:00"},
     {"id":24,"title":"v1.4.9 更新15AX|AT09|SPCE|TFSP新卡（16张）","url":"http://fff.ac/9tkwlv","created_at":"2015-01-25T19:34:06+08:00","updated_at":"2015-02-05T19:34:06+08:00"},