.travis.yml in link_thumbnailer-3.3.0 vs .travis.yml in link_thumbnailer-3.3.1

@@ -1,4 +1,5 @@
 bundler_args: --without development
 language: ruby
 rvm:
-  - 2.2.0
+  - 2.2.2
+  - 2.4.0