Root route should transition to `release` url structure

[toddjordan]

Right now going to the root route transitions to the first module in the latest release, https://emberjs.com/api/ember/2.18/modules/@ember%2Fapplication at the time of this issue creation. Transitioning to the release version of the url will help SEO, since web crawlers from emberjs.com would get the release version of the base url, which is always current, and prevent things like old hard coded versions showing up in api docs.

After the fix going to emberjs.com/api should go to https://emberjs.com/api/ember/release/modules/@ember%2Fapplication