Use https://www.virtualbox.org for all VirtualBox links

From an internal ticket:

> Just noticed that the Link to Virtualbox points to the not-www-Subdomain. And on that domain I got an https-error. If you change the link to the www-subdomain, there’s no error.

I believe the URL was being rewritten by the HTML compressor and upgrading Vagrant to middleman-hashicorp is a much bigger task than imagined :frowning:.