.travis.yml in redstream-0.1.1 vs .travis.yml in redstream-0.2.0

@@ -1,8 +1,9 @@
 sudo: false
 language: ruby
+cache: bundler
 rvm:
-  - ruby-head
+  - ruby-2.6.2
 before_install:
   - docker-compose up -d
   - sleep 10
 install:
   - travis_retry bundle install