Put the account name in the card title if the full name is not available

    Without this patch the author_name method of the GithubMix module will
    return nil if the full name of the account is not available.  This is a
    problem because the full name is often not available, for example:
    https://github.com/brunoleon does not have an email address, full name,
    or company, and the card titles look weird, like:

        (PR hiera/123) Interpolate hash keys like already done for strings. []

    This patch addresses the problem by returning the account name if the
    full name is not available, so the card title looks better.  For
    example:

        (PR hiera/123) Interpolate hash keys like already done for strings. [brunoleon]