MDL-36621 cache: added missing calendar subscription string

lang/en/cache.php

@@ -34,6 +34,7 @@
 $string['caching'] = 'Caching';
 $string['cacheadmin'] = 'Cache administration';
 $string['cacheconfig'] = 'Configuration';
+$string['cachedef_calendar_subscriptions'] = 'Calendar subscriptions';
 $string['cachedef_config'] = 'Config settings';
 $string['cachedef_databasemeta'] = 'Database meta information';
 $string['cachedef_eventinvalidation'] = 'Event invalidation';