Added volume to docker-compose-cassandra in order to support data persistency
Added volume to docker-compose-cassandra in order to support data persistency

Signed-off-by: nmarcetic <563861f1f7644bdda2dd6c3cebfddd9ab6b313f0@gmail.com>

drasko/mainflux,drasko/mainflux,Mainflux/mainflux-lite,drasko/mainflux