Add mongodb to travis. It is needed for the tests.
Add mongodb to travis. It is needed for the tests.

njam/pulsar-rest-api,njam/pulsar-rest-api,njam/pulsar-rest-api,cargomedia/pulsar-rest-api,njam/pulsar-rest-api,vogdb/pulsar-rest-api,cargomedia/pulsar-rest-api,cargomedia/pulsar-rest-api,cargomedia/pulsar-rest-api,vogdb/pulsar-rest-api,vogdb/pulsar-rest-api