The current installer script, has a hard coded reference to the latest node version: https://github.com/MichMich/MagicMirror/blob/v2-beta/installers/raspberry.sh#L21
This means that whenever a new Node version is released, the installer breaks until we update the version reference.
If somebody knows a good way to solve this, feel free to send a pull request.
And while you’re at it. It might be a good idea to only install Node when it’s not present or below a certain version (v5).