fix(app): disable app downgrade feature

Ensure that we set electron-updater `allowDowngrade=false` after
setting the update channel, since `autoUpdater.channel` is a setter
which explicity sets `allowDowngrade=true`.

electron/updater.js

@@ -59,8 +59,8 @@ class ZapUpdater {
   configure(settings) {
     Object.assign(this.settings, settings)
 
-    autoUpdater.allowDowngrade = false
     autoUpdater.channel = this.settings.channel
+    autoUpdater.allowDowngrade = false
   }
 
   /**