.travis.yml in hako-0.20.2 vs .travis.yml in hako-0.20.3

@@ -1,10 +1,8 @@
 language: ruby
 sudo: false
 rvm:
-  - 2.1.8
-  - 2.2.4
-  - 2.3.0
+  - 2.3.1
   - ruby-head
 before_install:
   - gem install bundler
 matrix:
   allow_failures: