.travis.yml in kindlegen-2.9.5 vs .travis.yml in kindlegen-2.9.6

@@ -1,7 +1,8 @@
 language: ruby
+sudo: false
+cache: bundler
 rvm:
-  - 2.1.5
-  - 2.2.0
-  - 2.2.1
+  - 2.1.7
+  - 2.2.3
 # NOTE the build step is required to run the tests
 script: bundle exec rake build test