Add config/database.travis.yml

https://www.pivotaltracker.com/story/show/66555850

Specs are failing on CI because Travis is trying to use postgres but it should be using sqlite. Still investigating.

> /home/travis/build/G5/g5-hub/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.12/lib/active_record/connection_adapters/postgresql_adapter.rb:1208:in `initialize': FATAL: database "g5-hub_test" does not exist (PG::Error)

https://travis-ci.org/G5/g5-hub/builds/19889649#L215