Fix .desktop file to comply with FDO specifications.

--- a/xye.desktop
+++ b/xye.desktop
@@ -4,11 +4,11 @@
 Encoding=UTF-8
 Exec=xye
 Type=Application
-Categories=Application;Game;PuzzleGame
+Categories=Game;LogicGame
 Name=Xye
 GenericName=Xye
 Comment=Solve puzzles and action challenges in order to get all the gems in the room.
 Terminal=false
 StartupNotify=false
-Icon=xye.png
+Icon=xye
 MimeType=application/xye-xml