Upgrade ember-electron from 4.2.2 to 6.0.0 (#2740)

* Upgrade to ember-electron 6

ui/desktop/package.json

@@ -77,7 +77,7 @@
     "ember-cli-sri": "^2.1.1",
     "ember-cli-terser": "^4.0.2",
     "ember-concurrency": "^4.0.3",
-    "ember-electron": "^4.2.2",
+    "ember-electron": "^6.0.0",
     "ember-exam": "^8.0.0",
     "ember-inline-svg": "^1.0.1",
     "ember-load-initializers": "^2.1.2",