ci/travis: update xcode version to 8.3
ci/travis: update xcode version to 8.3

Xcode version: 8.3.3
macOS version: 10.12

Signed-off-by: Koichi Shiraishi <2e5bdfebde234ed3509bcfc18121c70b6631e207@gmail.com>

zchee/docker-machine-driver-xhyve,zchee/docker-machine-driver-xhyve