Fix html id

Author: remcoder

demo/index.html

@@ -108,8 +108,8 @@ <h1 class="text-center m-3 mb-5">GCode Preview
                   <input type="checkbox" id="single-layer-mode" v-model="settings.singleLayerMode" />
                 </div>
                 <div class="controls">
-                  <label for="single-layer-mode">Animate layers</label>
-                  <input type="checkbox" id="single-layer-mode" v-model="loadProgressive" />
+                  <label for="animate-layers">Animate layers</label>
+                  <input type="checkbox" id="animate-layers" v-model="loadProgressive" />
                 </div>
               </section>
               <section v-else>