Fix typo in a db:rollback script (#5422)

Reported at
https://don.inux39.me/@inux39/1406082
https://don.inux39.me/@inux39/1406134

db/migrate/20170920024819_status_ids_to_timestamp_ids.rb

@@ -26,7 +26,7 @@ class StatusIdsToTimestampIds < ActiveRecord::Migration[5.1]
       SELECT setval('statuses_id_seq', (SELECT MAX(id) FROM statuses));
       ALTER TABLE statuses
         ALTER COLUMN id
-        SET DEFAULT nextval('statuses_id_seq');"
+        SET DEFAULT nextval('statuses_id_seq');
     SQL
   end
 end