'The filename that corresponds to the specified version and kind.
.. warning:: The specified version may not exist in this
lineage. There is no guarantee that the file path returned
by this method actually exists.
:param str kind: the lineage member item ("cert", "privkey",
"chain", or "fullchain")
:param int version: the desired version
:returns: The path to the specified version of the specified member.
:rtype: str'

def version(self, kind, version):

    if (kind not in ALL_FOUR):
        raise errors.CertStorageError('unknown    kind    of    item')
    where = os.path.dirname(self.current_target(kind))
    return os.path.join(where, '{0}{1}.pem'.format(kind, version))
