.travis.yml in kan-0.1.0 vs .travis.yml in kan-0.2.0

@@ -1,5 +1,13 @@
 sudo: false
 language: ruby
+cache: bundler
 rvm:
+  - 2.1.10
+  - 2.2.7
+  - 2.3.4
   - 2.4.1
-before_install: gem install bundler -v 1.16.0
+  - 2.5.0
+
+before_install:
+  - gem install bundler -v 1.16.0
+  - gem update --system