ci(travis): add notifications => zulip [skip ci]

.travis.yml

@@ -110,9 +110,21 @@ after_success:
       fi
     fi
 
+# Notification options: `always`, `never` or `change`
 notifications:
   irc:
     channels:
       - 'chat.freenode.net#salt-image-builder'
-    on_success: always
-    on_failure: always
+    on_success: always  # default: always
+    on_failure: always  # default: always
+    on_start: always    # default: never
+    on_cancel: always   # default: always
+    on_error: always    # default: always
+  webhooks:
+    urls:
+      - https://saltstack-formulas.zulipchat.com/api/v1/external/travis?api_key=HsIq3o5QmLxdnVCKF9is0FUIpkpAY79P&stream=CI&topic=salt-image-builder&ignore_pull_requests=false
+    on_success: always  # default: always
+    on_failure: always  # default: always
+    on_start: always    # default: never
+    on_cancel: always   # default: always
+    on_error: always    # default: always