Bug in far checking in superevents.py

There is a bug in https://git.ligo.org/emfollow/gwcelery/blob/master/gwcelery/tasks/superevents.py#L45 The operation is

if far > far_threshold:
    log.info('Skipping')
    return

Minor change, but currently causing superevent_manager to ignore all new type signoficant MDCs