Update rubocop and enable in CI (#197)

Several of the Rubocop cop definitions have been renamed or moved to
entirely other gems. This brings the configuration up to date with the
latest naming conventions.

Author: keelerm84

.circleci/config.yml

@@ -1,9 +1,16 @@
 version: 2.1
 
+orbs:
+  rubocop: hanachin/rubocop@0.0.6
+
 workflows:
   version: 2
   test:
     jobs:
+      - rubocop/rubocop:
+          after-install-rubocop:
+            - run: gem install rubocop-performance
+            - run: gem install rubocop-rails
       - build-test-linux:
           name: Ruby 2.6
           docker-image: cimg/ruby:2.6