use explicit autoloads rather than from paths

Procfile

@@ -1,6 +1,6 @@
 web: bundle exec puma -C config/puma.rb
 fast: bundle exec rake postal:fast_server
-worker: bundle exec rake postal:worker
+worker: bundle exec ruby script/worker.rb
 cron: bundle exec rake postal:cron
 smtp: bundle exec rake postal:smtp_server
 requeuer: bundle exec rake postal:requeuer