.travis.yml in slack-ruby-client-0.11.1 vs .travis.yml in slack-ruby-client-0.12.0

@@ -2,11 +2,11 @@
 
 cache: bundler
 
 rvm:
   - 2.2
-  - 2.1
-  - 2.3.4
+  - 2.3
+  - 2.5
   - ruby-head
   - jruby-head
 
 matrix:
   include: