.travis.yml in howitzer-2.0.1 vs .travis.yml in howitzer-2.0.2

@@ -1,6 +1,7 @@
 language: ruby
 before_install:
   - gem install bundler
-rvm:  
-  - 2.2.5
-  - 2.3.1
+rvm:
+  - 2.2.6
+  - 2.3.3
+  - 2.4.0