Update to latest freedesktop spec.

--- data/qalculate-gtk.desktop.in
+++ data/qalculate-gtk.desktop.in
@@ -1,11 +1,9 @@
 [Desktop Entry]
-Encoding=UTF-8
 _Name=Qalculate!
 _Comment=Powerful and easy to use calculator
 Exec=qalculate-gtk
-Icon=qalculate.png
+Icon=qalculate
 Terminal=false
 Type=Application
 StartupNotify=true
-Categories=GNOME;Application;Utility;
-
+Categories=GTK;Utility;