yarnpkg.com --> classic.yarnpkg.com (#1133)

* yarnpkg.com --> classic.yarnpkg.com

This will update `<link rel="canonical">` (via https://github.com/yarnpkg/website/blob/5be62ee/_layouts/default.html ), so Google Search will show "classic" URL. Intent is to reduce confusion re: Yarn 1 vs Yarn 2 docs. See yarnpkg/berry#3425

* Package detail pages: add "classic" subdomain to permalink

This will update `<link rel="canonical">`, so Google Search will show "classic" URL, for pages like https://classic.yarnpkg.com/en/package/Babel . Intent is to reduce confusion re: Yarn 1 vs Yarn 2 docs. See yarnpkg/berry#3425
(Also updates `<meta property="og:url"]`)

Author: mrienstra

_config.yml

@@ -3,7 +3,7 @@ title: Yarn
 description: > # this means to ignore newlines until "baseurl:"
   Fast, reliable, and secure dependency management.
 baseurl: ""
-url: "https://yarnpkg.com"
+url: "https://classic.yarnpkg.com"
 twitter_username: yarnpkg
 github_username:  yarnpkg
 

js/src/components/Details.js

@@ -22,7 +22,7 @@ const readmeErrorMessage = 'ERROR: No README data found!';
 
 function setHead({ name, description }) {
   const head = document.querySelector('head');
-  const permalink = `https://yarnpkg.com${packageLink(name)}`;
+  const permalink = `https://classic.yarnpkg.com${packageLink(name)}`;
   head.querySelector('meta[property="og:title"]').setAttribute('content', name);
   document.title = `${name} | Yarn`;
   head