chore: remove duplicate character in index.html

https://github.com/opensheetmusicdisplay/opensheetmusicdisplay/issues/1457

demo/index.html

@@ -32,7 +32,7 @@
         <h3 class="ui header">Render backend:</h3>
         <select class="ui selection dropdown" id="backend-select" value="svg" style="height:38%; visibility: hidden;">
             <option value="svg">SVG</option>
-            <option value="canvas">Canvas</option>>
+            <option value="canvas">Canvas</option>
         </select>
     </div>
     <div class="column">