Add slack notification

Author: pbrisbin

Diff for: circle.yml

@@ -30,3 +30,6 @@ deployment:
       - docker tag $registry_root/$CIRCLE_PROJECT_REPONAME:b$CIRCLE_BUILD_NUM $CODECLIMATE_DOCKER_REGISTRY_HOSTNAME/$CIRCLE_PROJECT_USERNAME/$CIRCLE_PROJECT_REPONAME:b$CIRCLE_BUILD_NUM
       - docker push $CODECLIMATE_DOCKER_REGISTRY_HOSTNAME/$CIRCLE_PROJECT_USERNAME/$CIRCLE_PROJECT_REPONAME:b$CIRCLE_BUILD_NUM
 
+notify:
+  webhooks:
+    - url: https://cc-slack-proxy.herokuapp.com/circle