Fix JavaScript style

lib/browser/guest-window-manager.js

@@ -243,7 +243,9 @@ ipcMain.on('ELECTRON_GUEST_WINDOW_MANAGER_INTERNAL_WINDOW_OPEN', function (event
                                                                   additionalFeatures, postData) {
   options = mergeBrowserWindowOptions(event.sender, options)
   const newWindowEvent = {
-    preventDefault: () => newWindowEvent.defaultPrevented = true
+    preventDefault: function () {
+      this.defaultPrevented = true
+    }
   }
   event.sender.emit('new-window', newWindowEvent, url, frameName, disposition, options, additionalFeatures)
   const newGuest = newWindowEvent.newGuest