Merge pull request #423 from nicolasleger/test-ruby-versions

Test on new Ruby versions

Author: rafaelfranca

.travis.yml

@@ -11,9 +11,10 @@ rvm:
   - 1.9
   - 2.0
   - 2.1
-  - 2.2.8
-  - 2.3.5
-  - 2.4.2
+  - 2.2
+  - 2.3.6
+  - 2.4.3
+  - 2.5.0
   - ruby-head
   - jruby-19mode
   - rbx