[Minor] Notify coveralls when build is over

.circleci/config.yml

@@ -152,6 +152,10 @@ jobs:
       - *restore_coverage_data
       - *merge_and_upload_coverage_data
 
+notify:
+  webhooks:
+    - url: https://coveralls.io/webhook?repo_token={{ .Environment.COVERALLS_REPO_TOKEN }}
+
 workflows:
   version: 2
   build-and-test: