Set Codecov upload file in CircleCI

Update the CircleCI pipeline to pass `coverage/.resultset.json` to the `codecov/upload` step, so coverage uploads use the expected report artifact explicitly.

Author: bradpotts

.circleci/config.yml

@@ -29,7 +29,8 @@ jobs:
       - store_test_results:
           path: tmp/test-results
       - run: bundle exec rubocop
-      - codecov/upload
+      - codecov/upload:
+          file: coverage/.resultset.json
 
 workflows:
   test: