.travis.yml in review-2.0.0 vs .travis.yml in review-2.1.0

@@ -6,10 +6,11 @@
 
 rvm:
   - 2.0.0
   - 2.1.*
   - 2.2.*
-  - 2.3.0
+  - 2.3.1
+##  - ruby-head
 
 addons:
   apt_packages:
     - libgmp3-dev