travis: fix versions and unzip verbosity
travis: fix versions and unzip verbosity

Don't pin to specific minor releases: just 1.6 and 1.7 is fine.

Make the unzipping quiet, since printing all the file names clogs up the
logs.

Change-Id: I256ae1221cc64a05cc89438102454c574da23a87

golang/appengine,fuchsia-mirror/third_party-github.com-golang-appengine,golang/appengine,fuchsia-mirror/third_party-github.com-golang-appengine