Merge pull request #21 from github/dependabot/bundler/rubocop-rails-2.21.2

Bump rubocop-rails from 2.15.2 to 2.21.2

Author: khiga8

Gemfile.lock

@@ -90,10 +90,10 @@ GEM
     rubocop-performance (1.19.1)
       rubocop (>= 1.7.0, < 2.0)
       rubocop-ast (>= 0.4.0)
-    rubocop-rails (2.15.2)
+    rubocop-rails (2.21.2)
       activesupport (>= 4.2.0)
       rack (>= 1.1)
-      rubocop (>= 1.7.0, < 2.0)
+      rubocop (>= 1.33.0, < 2.0)
     ruby-progressbar (1.13.0)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)