Fix QA violations in desktop file

--- a/sirius.desktop.in
+++ b/sirius.desktop.in
@@ -3,7 +3,7 @@
 _Name=Sirius
 _Comment=Sirius, a othello playing program
 Exec=sirius
-Icon=sirius.png
+Icon=sirius
 Terminal=false
 Type=Application
-Categories=GNOME;Application;Game;
+Categories=GNOME;Game;