chore(travis) bump Cassandra version
chore(travis) bump Cassandra version

2.1.9 has been released, and 2.1.8 is not available to download
anymore...

kyroskoh/kong,ejoncas/kong,shiprabehera/kong,ccyphers/kong,ajayk/kong,isdom/kong,Mashape/kong,rafael/kong,Vermeille/kong,smanolache/kong,salazar/kong,kyroskoh/kong,Kong/kong,Kong/kong,vzaramel/kong,li-wl/kong,jerizm/kong,isdom/kong,beauli/kong,ejoncas/kong,Kong/kong,xvaara/kong,rafael/kong,vzaramel/kong,jebenexer/kong,icyxp/kong,akh00/kong