Updated tk-desktop to v2.8.5

Release notes: https://github.com/shotgunsoftware/tk-desktop/releases/tag/v2.8.5

Author: toolkitty-app[bot]

env/includes/engine_locations.yml

@@ -28,7 +28,7 @@ engines.tk-alias.location:
 engines.tk-desktop.location:
   type: app_store
   name: tk-desktop
-  version: v2.8.4
+  version: v2.8.5
 engines.tk-desktop2.location:
   type: app_store
   name: tk-desktop2