.travis.yml in japanese_calendar-0.3.1 vs .travis.yml in japanese_calendar-0.3.2

@@ -1,8 +1,11 @@
 sudo: false
 language: ruby
 rvm:
-- 2.3.3
+  - 2.1.10
+  - 2.2.6
+  - 2.3.3
+  - 2.4.0
 before_install: gem install bundler -v 1.13.6
 addons:
   code_climate:
     repo_token: c542293583b86ca95015675c334c9fea63c14825709f7c9eb4c72a0c8cfc71b4
 after_success: