delayedjob-gemfile - lock to lower version of delayed_job_active_record

Avoids error:

PG::Error: ERROR:  SELECT FOR UPDATE/SHARE is not allowed in subqueries
: UPDATE "delayed_jobs" SET locked_at = '2013-04-10 17:24:34.380950', locked_by = 'host:tomckay.csb pid:3167' WHERE id IN (SELECT  id FROM "delayed_jobs"  WHERE ((run_at <= '2013-04-10 17:24:34.372213' AND (locked_at IS NULL OR locked_at < '2013-04-10 13:24:34.372230') OR locked_by = 'host:tomckay.csb pid:3167') AND failed_at IS NULL) ORDER BY priority ASC, run_at ASC LIMIT 1 FOR UPDATE) RETURNING *

w/ postgresql 8.4.13 on RHEL