.travis.yml in slack-ruby-client-0.6.0 vs .travis.yml in slack-ruby-client-0.7.0

@@ -1,9 +1,10 @@
 language: ruby
 
 cache: bundler
 
 rvm:
+  - 2.3.0
   - 2.2
   - 2.1
   - 2.0
   - rbx-2
   - jruby-19mode