update deployed URL in doc

[alpapan]

The URL in the README is drupalvm.test but the current version now serves at drupalvn.dev (as correctly notified by the vagrant file)

thanks!

[oxyc]

It's a bit unfortunate but the current README on GitHub always points the the development branch rather than the current stable release. I think I read @geerlingguy comment on this somewhere and back then he wasn't interested in switching the git workflow model. Even if the current model has it's shortcomings, it's far simpler to maintain.

[geerlingguy]

Yeah, sorry about that! I'll be creating a release very soon: #1573