Travis: don't generate git clone progress for logs

The logs are usually not looked at, and when they are it's almost
always after they've completed and returned a status.  That being
the case, "progress" output is useless if it's always seen after
the fact.

Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com>

Reviewed-by: Andy Polyakov <appro@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6928)