transport-helper: Use capname for refspec capability too

transport-helper: Use capname for refspec capability too

Previously the refspec capability could not be listed as
required or their parsing would break.

Most likely the reason the second hunk wasn't caught is because the
series that added 'refspec' as capability, and the one that added
required capabilities were done in parallel.

Signed-off-by: Sverre Rabbelier <srabbelier@gmail.com>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>