Bump ruby version used in CI

sciurus · sciurus · commit dea17ad3955e · 2018-09-12T16:29:31.000-04:00
diff --git a/.travis.yml b/.travis.yml
@@ -2,4 +2,4 @@ language: ruby
 sudo: false
 cache: bundler
 rvm:
-  - 2.2.1
+  - 2.5.1
