.travis.yml in oak-0.4.1 vs .travis.yml in oak-0.4.2

@@ -2,12 +2,14 @@
 language: ruby
 before_install:
   - gem install bundler -v 1.16.1
 rvm:
   - 2.1.6
-  - 2.2.9
-  - 2.4.3
-  - 2.5.0
+  - 2.2.7
+  - 2.2.10
+  - 2.3.7
+  - 2.4.4
+  - 2.5.1
 script:
   #
   # Run several tests in parallel, and be happy if they are all happy.
   #
   # If any fail, rerun serially so we get clean output from the ones