.travis.yml in rack-component-0.4.2 vs .travis.yml in rack-component-0.5.0

@@ -1,6 +1,8 @@
 ---
 language: ruby
 cache: bundler
 rvm:
-  - 2.5.1
+  - 2.5.3
+  - 2.4
+  - 2.3
 before_install: gem install bundler -v 1.16.5