.travis.yml in graphql-batch-0.3.5 vs .travis.yml in graphql-batch-0.3.7

@@ -1,5 +1,7 @@
 language: ruby
 rvm:
   - 2.1
   - 2.2
+  - 2.3
+  - 2.4
 before_install: gem install bundler -v 1.13.3