Docs: Replace cdn (#9040)

* fix: Replace cdn

* fix: Correct cdn host

examples/index.tpl

@@ -11,7 +11,7 @@
     <div id="app"></div><% if (process.env.NODE_ENV === 'production') { %>
     <script>
       if (!window.Promise) {
-        document.write('<script src="//shadow.elemecdn.com/npm/es6-promise@4.1.1/dist/es6-promise.min.js"><\/script><script>ES6Promise.polyfill()<\/script>')
+        document.write('<script src="//cdn.jsdelivr.net/npm/es6-promise@4.1.1/dist/es6-promise.min.js"><\/script><script>ES6Promise.polyfill()<\/script>')
       }
     </script>
     <script src="//cdn.jsdelivr.net/npm/vue@2.5.2/dist/vue.runtime.min.js"></script>