.travis.yml in require_smasher-0.3.1 vs .travis.yml in require_smasher-0.3.2

@@ -1,9 +1,14 @@
 sudo: false
 language: ruby
 rvm:
   - 2.3.1
+  - 2.3.7
+  - 2.4.0
+  - 2.4.4
+  - 2.5.1
 before_install:
   - gem install bundler -v 1.16.3
   - bundle install
 install:
   - bundle exec rspec
+  - bundle exec rubocop