fix(docs): correct polyfilling suggestions (#3605)

* fix(docs): polyfilling suggestions

* Update README.md

Author: jacobmllr95

docs/markdown/intro/README.md

@@ -494,7 +494,7 @@ JavaScript files.
 <link type="text/css" rel="stylesheet" href="//unpkg.com/bootstrap-vue@latest/dist/bootstrap-vue.min.css" />
 
 <!-- Load polyfills to support older browsers -->
-<script src="//polyfill.io/v3/polyfill.min.js?features=es2015%2CMutationObserver" crossorigin="anonymous"></script>
+<script src="//polyfill.io/v3/polyfill.min.js?features=es2015%2CIntersectionObserver" crossorigin="anonymous"></script>
 
 <!-- Load Vue followed by BootstrapVue -->
 <script src="//unpkg.com/vue@latest/dist/vue.min.js"></script>
@@ -551,34 +551,35 @@ Following features and APIs are used by BootstrapVue:
 - ES6 (e.g. `Array.from()`, `Array.isArray()`, `Object.assign()`, `Object.is()`, etc.)
 - `Promise`
 - `MutationObserver`
+- `IntersectionObserver` (optional)
 
 If you want to support older IE, Android and iOS devices, you may want to use
 [core-js](https://github.com/zloirock/core-js) and
-[mutationobserver-shim](https://www.npmjs.com/package/mutationobserver-shim):
+[intersection-observer](https://www.npmjs.com/package/intersection-observer):
 
-- `npm install core-js regenerator-runtime mutationobserver-shim`
+- `npm install core-js regenerator-runtime intersection-observer`
 - Import the polyfills in your app main entry point:
 
 <!-- eslint-disable no-unused-vars -->
 
 ```js
-import 'core-js/stable"'
+import 'core-js/stable'
 import 'regenerator-runtime/runtime'
-import 'mutationobserver-shim'
+import 'intersection-observer' // Optional
 import Vue from 'vue'
 import BootstrapVue from 'bootstrap-vue'
 ```
 
 If using deprecated [@babel/polyfill](https://babeljs.io/docs/en/babel-polyfill/):
 
-- `npm install @babel/polyfill mutationobserver-shim`
+- `npm install @babel/polyfill intersection-observer`
 - Import the polyfills in your app main entry point:
 
 <!-- eslint-disable no-unused-vars -->
 
 ```js
 import '@babel/polyfill'
-import 'mutationobserver-shim'
+import 'intersection-observer' // Optional
 import Vue from 'vue'
 import BootstrapVue from 'bootstrap-vue'
 ```

docs/markdown/reference/router-links/README.md

@@ -169,7 +169,10 @@ do not support IntersectionObserver, you can use the following conditional polyf
 export default {
   head: {
     script: [
-      { src: 'https://polyfill.io/v2/polyfill.min.js?features=IntersectionObserver', body: true }
+      {
+        src: 'https://polyfill.io/v3/polyfill.min.js?features=es2015%2CIntersectionObserver',
+        body: true
+      }
     ]
   }
 }

docs/nuxt.config.js

@@ -158,7 +158,7 @@ module.exports = {
     meta: [{ 'http-equiv': 'X-UA-Compatible', content: 'IE=edge' }],
     script: [
       {
-        src: '//polyfill.io/v3/polyfill.min.js?features=es2015%2CMutationObserver',
+        src: '//polyfill.io/v3/polyfill.min.js?features=es2015%2CIntersectionObserver',
         crossorigin: 'anonymous'
       }
     ]