fix(examples): fix missing polyfill in e-commerce demo (#4076)

Author: Yannick Croissant

examples/e-commerce/index.html

@@ -25,6 +25,7 @@
     <link rel="stylesheet" href="./src/app.css" />
     <link rel="stylesheet" href="./src/app.mobile.css" />
     <link rel="stylesheet" href="./src/widgets/PriceSlider.css" />
+    <script src="https://polyfill.io/v3/polyfill.min.js?features=default,Array.prototype.find,Array.prototype.includes"></script>
 
     <title>E-commerce demo | Algolia</title>
   </head>