add shim for selectedOptions for multiple select functionality

examples/index_ie11.html

@@ -19,10 +19,9 @@
     </style>
 
     <script
-        src="https://polyfill.io/v3/polyfill.min.js?features=MutationObserver%2CArray.from%2CArray.prototype.forEach%2CMap%2CSet%2CArray.prototype.includes%2CString.prototype.includes%2CPromise%2CNodeList.prototype.forEach%2CObject.values%2CReflect%2CReflect.set%2CString.prototype.startsWith%2CArray.prototype.find%2CArray.prototype.findIndex%2CElement.prototype.closest%2CElement.prototype.remove%2CCustomEvent">
+        src="https://polyfill.io/v3/polyfill.js?features=MutationObserver%2CArray.from%2CArray.prototype.forEach%2CMap%2CSet%2CArray.prototype.includes%2CString.prototype.includes%2CPromise%2CNodeList.prototype.forEach%2CObject.values%2CReflect%2CReflect.set%2CString.prototype.startsWith%2CArray.prototype.find%2CArray.prototype.findIndex%2CElement.prototype.closest%2CElement.prototype.remove%2CCustomEvent">
     </script>
-
-
+    <script src="https://unpkg.com/shim-selected-options" async></script>
     <script src="https://cdn.jsdelivr.net/npm/proxy-polyfill@0.3.0/proxy.min.js"></script>