Hm, like I said, anything I’m suggesting at this stage is purely experimental as I have no experience with setting up the MagicMirror electron environment, but you could try upgrading your node installation.
Please only do that if you are willing to set up your Pi all over again (Reinstalling Raspbian, etc.) should this fail, because it’s hardly ever a good idea to turn your system into a patchwork project.
Someone at stackexchange.com said this helped them in installing Node.js on their Pi 3:
curl -sL https://deb.nodesource.com/setup_6.x | sudo -E bash -
sudo apt-get install -y nodejs
sudo apt-get install -y build-essential
Source: http://raspberrypi.stackexchange.com/questions/45319/install-newer-node-version-on-pi-3
If you’re not willing to reinstall everything, should this compromise your Raspbian setup, I would suggest waiting for other forum members’ suggestions on how to proceed.