docs: ✏️ fix demo

Author: ttskch

docs/index.html

@@ -11,7 +11,7 @@
   <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/select2@4.0.13/dist/css/select2.min.css" integrity="sha256-FdatTf20PQr/rWg+cAKfl6j4/IY3oohFAJ7gVC3M34E=" crossorigin="anonymous">
 
   <!-- select2-bootstrap4-theme -->
-  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@ttskch/select2-bootstrap4-theme/dist/select2-bootstrap4.min.css" integrity="sha256-UfmOIikh6kg5BkHZRS0JbrlxjUKLY0uSgUt+4KJPw1M=" crossorigin="anonymous"> <!-- for live demo page -->
+  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@ttskch/select2-bootstrap4-theme/dist/select2-bootstrap4.min.css"> <!-- for live demo page -->
   <link href="select2-bootstrap4.css" rel="stylesheet"> <!-- for local development env -->
 </head>