Add mongodb under services in travis config
Add mongodb under services in travis config

kenzanboo/mail,rcaracaus/pa11y-api,ssmlee04/docker-user-module,sebasalvarado/dementia-hacks-api,wen911119/my-node-api,KunalKapadia/express-mongoose-es6-rest-api,maratgaip/MusicApi,ssmlee04/docker-user-module,KunalKapadia/express-mongoose-es6-rest-api