Order notifications by creation date

migrations/2018-05-24-100613_add_notifications_creation_date/down.sql

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+-- This file should undo anything in `up.sql`
+ALTER TABLE notifications DROP COLUMN creation_date;

migrations/2018-05-24-100613_add_notifications_creation_date/up.sql

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+-- Your SQL goes here
+ALTER TABLE notifications ADD COLUMN creation_date TIMESTAMP NOT NULL DEFAULT now();