Version up ruby 2.2.4

hirocaster · hirocaster · commit f0ae516856ef · 2015-12-20T21:32:45.000+09:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,9 +1,9 @@
 language: ruby
 install: bundle install --jobs=3 --retry=3
 rvm:
-  - 2.2.3
-  - 2.1.7
-  - 2.0.0-p647
+  - 2.2.4
+  - 2.1.8
+  - 2.0.0-p648
 gemfile:
   - Gemfile
   - ar41.gemfile
