ci: remove kube 1.16 from Travis CI
ci: remove kube 1.16 from Travis CI

As kube v1.18 is released we dont need to test
-2 version in our CI, removing the 1.16 testing
for the same reason.

Signed-off-by: Madhu Rajanna <60fbf37a92c2a0908e31296d18dadbec5a4dae17@gmail.com>

ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi