public function add(MigrationTrackerCapsule $capsule, MigrationCapsule $migration = null)
    {
        $capsules = $this->all();

        if (!is_null($migration)) {
            $capsule->addMigration($migration);
        }

        $capsules[] = $capsule;

        $this->write($capsules);

        return $capsules;
    }