update travis Github token env name

Author: embbnux

.travis.yml

@@ -22,7 +22,7 @@ deploy:
       repo: ringcentral/ringcentral-js-widget
   - provider: pages
     skip_cleanup: true
-    github_token: $RELEASE_TOKEN
+    github_token: $GITHUB_PAGES_TOKEN
     local_dir: ../docs/gh-pages
     email: '[email protected]'
     name: 'RingCentral Integrations Team'