community/dcron: remove bug where cron.update is not picked up while jobs are still running

Bug occurs when job runs a long time. The file cron.update will not be picked up until all jobs is completed.

This merge request contains original fix from dcron's repository: https://github.com/dubiousjim/dcron/commit/abf8c4bf53a84ef3de530519a3bbb6b599595f2c