.travis.yml in airborne-0.2.13 vs .travis.yml in airborne-0.3.0

@@ -1,10 +1,11 @@
 sudo: false
 language: ruby
 rvm:
-  - 2.2.3
-  - 2.3.1
-  - 2.4.1
+  - 2.3.3
+  - 2.4.2
+  - 2.5.3
+  - 2.6.0
 
 script: bundle exec rspec spec
 before_install:
   - gem update --system
   - gem --version