chore(.travis.yml): add travis notifications to gitchat

.travis.yml

@@ -13,3 +13,12 @@ sudo: false
 cache:
   directories:
     - node_modules
+
+# hooks
+notifications:
+  webhooks:
+    urls:
+      - https://webhooks.gitter.im/e/e369617839852624aa69
+    on_success: change  # options: [always|never|change] default: always
+    on_failure: always  # options: [always|never|change] default: always
+    on_start: false     # default: false