.travis.yml in jekyll-postcss-0.2.1 vs .travis.yml in jekyll-postcss-0.2.2

@@ -1,7 +1,10 @@
 ---
 sudo: false
 language: ruby
 cache: bundler
 rvm:
-  - 2.5.3
+  - 2.3.8
+  - 2.4.6
+  - 2.5.5
+  - 2.6.3
 before_install: gem install bundler -v 1.17.1