contrib/examples/git-clone.sh: avoid "test <cond> -a/-o <cond>"

The construct is error-prone; "test" being built-in in most modern shells, the reason to avoid "test <cond> && test <cond>" spawning one extra process by using a single "test <cond> -a <cond>" no longer exists. Signed-off-by: Elia Pinto <gitter.spiros@gmail.com> Reviewed-by: Matthieu Moy <Matthieu.Moy@imag.fr> Signed-off-by: Junio C Hamano <gitster@pobox.com>