sharenix: use freedesktop notifications instead of GTK ones

scripts/sharenix.fish

@@ -6,7 +6,9 @@ function run_spectacle
    spectacle -b $argv -n -o "$f"
 
    if test -f "$f"
-      sharenix -n -s Greyserv "$f"
+      if sharenix -s Greyserv "$f"
+         notify-send -u low -a sharenix -i dialog-information -c transfer.complete "Upload completed"
+      end
    end
 
    rm "$f"