.travis.yml in materialist-2.3.1 vs .travis.yml in materialist-3.0.0

@@ -2,8 +2,8 @@
 cache: bundler
 services:
   - redis-server
 rvm:
   - 2.4.0
-  - ruby-head
+  - 2.5.0
 script:
   - bundle exec rspec