[TASK] add travis webhook for gitter

.travis.yml

@@ -4,3 +4,10 @@ node_js:
 script: npm test --coverage
 after_success:
 - npm run coveralls
+notifications:
+  webhooks:
+    urls:
+      - https://webhooks.gitter.im/e/d1ec4245f90231619d30
+    on_success: change  # options: [always|never|change] default: always
+    on_failure: always  # options: [always|never|change] default: always
+    on_start: false     # default: false