.travis.yml in jekyll-diagrams-0.4.0 vs .travis.yml in jekyll-diagrams-0.4.1

@@ -1,4 +1,7 @@
 language: ruby
 rvm:
-  - 2.3.0
-before_install: gem install bundler -v 1.11.2
+  - 2.3.7
+  - 2.4.4
+  - 2.5.1
+
+before_install: gem install bundler