ci: use container-based builds on travis-ci.
ci: use container-based builds on travis-ci.

See: http://docs.travis-ci.com/user/migrating-from-legacy/

chenwenbin928/rabbitmq-c,chenwenbin928/rabbitmq-c,alanxz/rabbitmq-c,sakishum/rabbitmq-c,chenwenbin928/rabbitmq-c,soindy/rabbitmq-c,alanxz/rabbitmq-c,soindy/rabbitmq-c,sakishum/rabbitmq-c,alanxz/rabbitmq-c,sakishum/rabbitmq-c,Haster2004/rabbitmq-c,Haster2004/rabbitmq-c,Haster2004/rabbitmq-c,kilinrax/rabbitmq-c,kilinrax/rabbitmq-c,kilinrax/rabbitmq-c,soindy/rabbitmq-c