.travis.yml in r2-oas-0.1.3 vs .travis.yml in r2-oas-0.2.0

@@ -4,10 +4,12 @@
 language: ruby
 
 cache: bundler
 
 rvm:
-  - 2.3.3
+  - 2.5.1
+  - 2.5.7
+  - 2.6.5
 
 before_install: gem install bundler -v 1.17.3
 
 gemfile:
   - Gemfile