circle.yml in deka_eiwakun-0.4.0 vs circle.yml in deka_eiwakun-0.5.0

@@ -1,14 +1,15 @@
 dependencies:
   pre:
+    - gem update --system
     - gem update bundler
 
 machine:
   timezone:
     Asia/Tokyo
   ruby:
     version:
-      2.3.0
+      2.4.1
 
 test:
   override:
     - bundle exec rake rubocop