.travis.yml in dentaku-3.1.0 vs .travis.yml in dentaku-3.2.0

@@ -1,11 +1,12 @@
 language: ruby
 sudo: false
 rvm:
   - 2.0.0-p648
   - 2.1.10
-  - 2.2.8
-  - 2.3.5
-  - 2.4.2
+  - 2.2.9
+  - 2.3.6
+  - 2.4.3
+  - 2.5.0
 before_install:
   - gem update bundler
   - gem update --system