Add log message for dummy migration 18

js/modules/migrations/migrations_1_database_without_attachment_data.js

@@ -6,6 +6,7 @@ exports.migrations = [
     version: 18,
     async migrate(transaction, next) {
       console.log('Migration 18');
+      console.log('Attachments stored on disk');
       next();
     },
   },