Bump ruby version.

ggreer · ggreer · commit 604191736e1a · 2019-02-18T16:10:07.000-08:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,7 +1,7 @@
 language: ruby
 
 rvm:
-- 2.2
+- 2.4
 
 before_script: bundle update
 script: "script/test"
