Make the ruby linking error go away.

The core issue was that if you don't provide an install step travis
tries to do its default action which generates a bunch of ruby code
that is linked to the ruby on the host system instead of the ruby in
the container.

.travis.yml

@@ -7,9 +7,7 @@ language: ruby
 rvm:
   - "1.9.3"
 
-cache: bundler
-
-before_install:
+install:
   - docker-compose -f docker-compose-travis.yml up -d
 
 script:

.travis/run_tests.sh

 #!/bin/bash -xe
 . /edx/app/forum/forum_env
-. /edx/app/forum/ruby_env
 export MONGOHQ_URL="mongodb://mongo.edx:27017/cs_comments_service_test"
 
 cd /edx/app/forum/cs_comments_service
 
-gem update bundler # Ensure we use the latest version of bundler. Travis' default version of outdated.
-
 bundle install
 
 bundle exec rspec