.travis.yml in to_duration-1.1.1 vs .travis.yml in to_duration-1.2.0

@@ -1,5 +1,8 @@
 sudo: false
 language: ruby
 rvm:
-  - 2.3.2
-before_install: gem install bundler -v 1.13.6
+  - 2.2.10
+  - 2.3.7
+  - 2.4.4
+  - 2.5.1
+before_install: gem install bundler -v '~> 1.16'