.travis.yml in howitzer-2.0.3 vs .travis.yml in howitzer-2.1.0

@@ -1,7 +1,7 @@
 language: ruby
 before_install:
   - gem install bundler
 rvm:
-  - 2.2.7
-  - 2.3.4
-  - 2.4.1
+  - 2.2.8
+  - 2.3.5
+  - 2.4.2