Changed Polyfill provider domain

Following Cloudflare best practices we've switched out polyfill provider to their services. While in the long term I don't really trust using external services, I have to be honest and say that I don't know what removing polyfill will do for backwards compatibility with older browsers, which I want to maintain as best as possible. For now, I make this change!

Reccomendations gathered from here https://blog.cloudflare.com/automatically-replacing-polyfill-io-links-with-cloudflares-mirror-for-a-safer-internet

pages/index.vue

@@ -13,7 +13,7 @@ useHead({
   link: [{ rel: 'icon', type: 'image/png', href: '/favicon.png' }],
   script: [
     {
-      src: 'https://polyfill.io/v3/polyfill.min.js?features=default%2Ces2015%2Ces6%2Ces5',
+      src: 'https://cdnjs.cloudflare.com/polyfill/v3/polyfill.min.js?features=default%2Ces2015%2Ces6%2Ces5',
       crossorigin: 'anonymous',
     },
   ],