Bug 1499590 - Add periodic-file-updates task to .cron.yml. r=darktrojan,dustin a=jorgk Added configuration for periodic-file-updates task to comm's .cron.yml. This cron task mirrors one found in mozilla- repositories, and was part of comm-'s buildbot configuration that needed to be moved to Taskcluster. This is a reapply of an old patch. I've removed the comm-beta and comm-esr60 repositories from the configuration. Differential Revision: https://phabricator.services.mozilla.com/D15108

{
  "phabricator.uri" : "https://phabricator.services.mozilla.com/",
  "repository.callsign": "COMMCENTRAL"
}