'Returns whether or not the given mode_slug is eligible for a
certificate. Currently all modes other than \'audit\' grant a
certificate. Note that audit enrollments which existed prior
to December 2015 *were* given certificates, so there will be
GeneratedCertificate records with mode=\'audit\' which are
eligible.'

@classmethod
def is_eligible_for_certificate(cls, mode_slug):

    return (mode_slug != cls.AUDIT)
