I try to start it directly from the prompt
npm install electron --save-dev
electron@1.4.12 postinstall /home/pi/MagicMirror/node_modules/electron
node install.jsmagicmirror@2.0.0 /home/pi/MagicMirror
├── electron@1.4.12
└── UNMET PEER DEPENDENCY grunt@1.0.1npm WARN grunt-yamllint@0.2.0 requires a peer of grunt@~0.4.0 but none was installed.