Update '.drone.yml'

.drone.yml

@@ -30,6 +30,16 @@ steps:
   - docker push "$DOCKER_USERNAME/producer"
   - docker push "$DOCKER_USERNAME/producer:$DRONE_BUILD_NUMBER"
 
+- name: slack
+  image: plugins/slack
+  settings:
+    webhook:
+      from_secret: slack_webhook
+    channel: alerts-ci
+    icon_url: https://cloudcdn.tormakristof.eu/static/drone.svg
+  when:
+    status: [ failure ]
+
 services:
 - name: docker
   image: docker:stable-dind