.travis.yml in agnostic_backend-0.9.0 vs .travis.yml in agnostic_backend-0.9.1

@@ -1,7 +1,10 @@
 language: ruby
 rvm:
-  - 2.1.5
+  - "2.1.5"
+  - "2.1.8"
+  - "2.2.4"
+  - "2.3.0"
 script: bundle exec rspec spec
 branches:
   only:
     - master