Upgrade to Electron 6:

New version of Electron has enable by default sandbox
http://www.atom.pe/docs/api/sandbox-option/

There was some issues to migrate a new version of Electron for
MagicMirror. Using the new version in Travis CI was failing at this
time. The problem is because the testing runner is a Docker enviroment

The issue experimented is the same topic mentioned here:
 - https://github.com/electron/electron/issues/17972
 - https://github.com/electron-userland/spectron/issues/443

The fix for to all of this is to set the `--no-sandbox` mode in CI
testing https://electronjs.org/docs/all#--no-sandbox

This change use the feature to set and disable Sandbox using
by enviroment variable `ELECTRON_DISABLE_SANDBOX=1`
https://github.com/electron/electron/pull/16576

This change has reference #1800

.travis.yml

@@ -8,6 +8,7 @@ before_script:
  - yarn danger ci
  - npm install grunt-cli -g
  - "export DISPLAY=:99.0"
+ - "export ELECTRON_DISABLE_SANDBOX=1"
  - "sh -e /etc/init.d/xvfb start"
  - sleep 5
 script:

package.json

@@ -47,16 +47,16 @@
     "http-auth": "^3.2.3",
     "jsdom": "^11.6.2",
     "jshint": "^2.10.2",
-    "mocha": "^4.1.0",
+    "mocha": "^7.0.0",
     "mocha-each": "^1.1.0",
     "mocha-logger": "^1.0.6",
-    "spectron": "^3.8.0",
+    "spectron": "^8.0.0",
     "stylelint": "latest",
     "stylelint-config-standard": "latest",
     "time-grunt": "latest"
   },
   "optionalDependencies": {
-    "electron": "^3.0.13"
+    "electron": "^6.1.7"
   },
   "dependencies": {
     "colors": "^1.1.2",