Disables cassandra in travis to avoid perpetual build fail (#1357)
Disables cassandra in travis to avoid perpetual build fail (#1357)

Cassandra recently started crashing only in Travis (not CircleCI).
This removes cassandra from travis so that it doesn't keep breaking
the build.

fixes #1356
adriancole/zipkin,openzipkin/zipkin,adriancole/zipkin,twitter/zipkin,adriancole/zipkin,twitter/zipkin,twitter/zipkin,openzipkin/zipkin,adriancole/zipkin,openzipkin/zipkin,openzipkin/zipkin,openzipkin/zipkin,twitter/zipkin