lastFinishedAtDate addition

[AlexFrazer]

Good for scanning time zones. Eg:

const nextRun = SyncedCron.nextScheduledAtDate('send reminders');
const lastRun = SyncedCron.lastFinishedAtDate('send reminders');

Meteor.users.aggregate([
  { $match: { 'settings.reminders.enabled': true } },
  {
    $match: {
      'reminders.at': {
         $lte: nextRun,
         $gt: lastRun
      }
    }
  }
]).forEach(user => {
  // ...
});