I am getting the same issue with the black screen. When I access via localhost:8080, I get the default screen that tells you to create a config file. I was using a config.js file from an old build I did that worked, but I replaced it with the config file posted above and I get the same issue.
pi@n8MM:~/MagicMirror $ npm start
> magicmirror@2.1.1 start /home/pi/MagicMirror
> sh run-start.sh
Starting MagicMirror: v2.1.1
Loading config ...
Loading module helpers ...
No helper found for module: clock.
No helper found for module: compliments.
All module helpers loaded.
Starting server on port 8080 ...
Starting server op port 8080 ...
You're using a full whitelist configuration to allow for all IPs
Server started ...
Sockets connected & modules started ...
Launching application.
^C
pi@n8MM:~/MagicMirror $ node -v
v7.9.0
pi@n8MM:~/MagicMirror $ electron -v
v1.3.15
pi@n8MM:~/MagicMirror $