Updated tk-desktop to v2.5.9

Release notes: https://github.com/shotgunsoftware/tk-desktop/wiki/Release-Notes#v259

Author: Toolkitty

env/includes/common/engines.yml

@@ -75,7 +75,7 @@ common.engines.tk-vred.location:
 common.engines.tk-desktop.location:
   type: app_store
   name: tk-desktop
-  version: v2.5.8
+  version: v2.5.9
 
 # Desktop2
 common.engines.tk-desktop2.location: