nodejs-maven-plugin: allow usage of latest- version for nodeJs

We would like to use the Node 8.X LTS Releases in our project but don't want to update the version manually.

There is a "latest-8.x" folder on https://nodejs.org/dist/ available where the current release can be downloaded. It would be a nice addition, if this plugin supports this.

Note: this already works for the npmVersion as the parameter is directly passed to node.