Docs: duplicate ID in example

sky/examples/calculator/buttons.sky

 SKY MODULE - button widgets for calculator
 <!-- TODO(ianh): implement accessibility handling once the ax service exists -->
 
 <script>
   class AbstractButton extends Element {
     constructor (module) {
       super(module);
       let selector = new SelectorQuery('.dynamic');
       this.addEventListener('pointer-down', (event) => {
         selector.findAll(this.shadowRoot).every((element) => element.setAttribute('clicked'));
@@ skipping 25 matching lines @@
   <div class="dynamic" id="b">
    <div class="dynamic" id="c">
     <div class="dynamic" id="d">
      <content/>
     </div>
    </div>
   </div>
  </div>
 </template>
 
-<template id="threed-button-shadow-tree">
+<template id="flat-button-shadow-tree">
  <style>
   div { background: green; color: yellow; }
   div[clicked] { background: yellow; color: green; }
  </style>
  <div class=dynamic>
   <content/>
  </div>
 </template>
 
 <script>
@@ skipping 13 matching lines @@
      shadow: true,
      constructor: class extends AbstractButton {
        constructor (module) {
          super(module);
          this.shadowRoot.append(module.document.findId('flat-shadow-tree').cloneNode(true));
        }
      },
    }),
  };
 </script>