.travis.yml in gecko-ruby-0.6.0 vs .travis.yml in gecko-ruby-0.7.0

@@ -1,10 +1,9 @@
 language: ruby
 before_install:
  - gem install bundler
 rvm:
-  - 2.1
-  - 2.2
   - 2.3
   - 2.4
   - 2.5
+  - 2.6
   - ruby-head