Hopefully fix Windows shortcuts

* Revert https://github.com/vector-im/riot-web/commit/79d164309f7926cb1c24008e464a516d7a872325
   as it seems to break shortcuts altogether
 * Update electron-builder (and add the squirrel windows package
   that the newer version now requires: it's been split out). This
   uses a newer version of squirrel which has some fixes for
   shortcuts.

I'm unsure exactly what was going wrong originally in
https://github.com/vector-im/riot-web/issues/2775 but #79d1643
seems to break shortcut creation as far as I can see.

package.json

@@ -94,7 +94,8 @@
     "chokidar": "^1.6.1",
     "cpx": "^1.3.2",
     "css-raw-loader": "^0.1.1",
-    "electron-builder": "^10.4.1",
+    "electron-builder": "^11.2.4",
+    "electron-builder-squirrel-windows": "^11.2.1",
     "emojione": "^2.2.3",
     "expect": "^1.16.0",
     "fs-extra": "^0.30.0",