.travis.yml in null-logger-0.1.3 vs .travis.yml in null-logger-0.1.4

@@ -1,7 +1,11 @@
 language: ruby
 rvm:
   - 2.2.3
   - 2.3.0
   - 2.3.1
+  - 2.3.2
+  - 2.3.3
+  - 2.4.0
+  - 2.4.1
 script:
   - bundle exec rake