.travis.yml in test-kitchen-1.15.0 vs .travis.yml in test-kitchen-1.16.0

@@ -1,9 +1,10 @@
 language: ruby
 
 rvm:
-  - 2.2.5
-  - 2.3.1
+  - 2.2.6
+  - 2.3.3
+  - 2.4.0
   - ruby-head
 
 env:
   - global:
     - machine_user=travis