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: NPhilip Prindeville <philipp@redfish-solutions.com>
Reviewed-by: NAndy Polyakov <appro@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6928)

.travis.yml

@@ -7,6 +7,7 @@ language: c
 cache: ccache
 git:
     submodules: false
+    quiet: true
 
 before_install:
     - if [ -n "$COVERALLS" ]; then