appFavorite: Add missing .desktop extension for simplescan

Followup to cbecc1dbfd

One line changes are hard.. Was too focused on copy pasting the id
that I omitted the .desktop part.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2728>

js/ui/appFavorites.js

@@ -59,7 +59,7 @@ const RENAMED_DESKTOP_IDS = {
     'polari.desktop': 'org.gnome.Polari.desktop',
     'seahorse.desktop': 'org.gnome.seahorse.Application.desktop',
     'shotwell.desktop': 'org.gnome.Shotwell.desktop',
-    'simple-scan.desktop': 'org.gnome.SimpleScan',
+    'simple-scan.desktop': 'org.gnome.SimpleScan.desktop',
     'tali.desktop': 'org.gnome.Tali.desktop',
     'totem.desktop': 'org.gnome.Totem.desktop',
     'evince.desktop': 'org.gnome.Evince.desktop',