fix: recommend cloudflare vs polyfill.io

Author: titanism

README.md

@@ -47,7 +47,7 @@ console.log('M/D/YY', dayjs().format('M/D/YY'));
 This is the solution for you if you're just using `<script>` tags everywhere!
 
 ```html
-<script src="https://polyfill.io/v3/polyfill.min.js?features=Promise"></script>
+<script src="https://cdnjs.cloudflare.com/polyfill/v3/polyfill.min.js?features=Promise"></script>
 <script src="https://unpkg.com/dayjs-with-plugins"></script>
 <script type="text/javascript">
   (function() {
@@ -58,10 +58,10 @@ This is the solution for you if you're just using `<script>` tags everywhere!
 
 ##### Required Browser Features
 
-We recommend using <https://polyfill.io> (specifically with the bundle mentioned in [VanillaJS](#vanillajs) above):
+We recommend using <https://cdnjs.cloudflare.com/polyfill> (specifically with the bundle mentioned in [VanillaJS](#vanillajs) above):
 
 ```html
-<script src="https://polyfill.io/v3/polyfill.min.js?features=Promise"></script>
+<script src="https://cdnjs.cloudflare.com/polyfill/v3/polyfill.min.js?features=Promise"></script>
 ```
 
 * Promise is not supported in op\_mini all