Travis deploy to test instance

[bruntonspall]

We have two instances on cloudfoundary, production and sandbox. Currently the bot runs in the sandbox, for historical reasons.

The ideal workflow should be: Pull requests should be deployed to sandbox, configured to talk to mbs-bot-test.slack.com Merges to master should be deployed to production, configured to talk to ukgovernmentdigital.slack.com

This requires someone to configure travis properly, and ensure that the credentials are deployed into the environment appropriately.