Fix www.mtga.codes redirect

[schmich]

• https://www.mtga.codes should auto redirect to https://mtga.codes
• GitHub Pages + custom domains + TLS + www/apex redirects is not currently supported
  • See https://github.community/t5/GitHub-Pages/Does-GitHub-Pages-Support-HTTPS-for-www-and-subdomains/td-p/7116/page/4
  • See GitHub Pages: Generate SSL certificate for www subdomain when a custom domain is set to an apex (and vice versa) isaacs/github#1675
• Other articles
  • https://github.blog/2018-05-01-github-pages-custom-domains-https/
  • https://help.github.com/en/articles/managing-a-custom-domain-for-your-github-pages-site
  • https://help.github.com/en/articles/troubleshooting-custom-domains-and-github-pages