use PNG icon for desktop file (not everyone supports SVG yet)

share/applications/feh.pre

@@ -4,7 +4,7 @@ Comment=Fast Imlib2-based Image Viewer
 Exec=feh %f
 Terminal=false
 Type=Application
-Icon=$IMAGEDIR$/logo.svg
+Icon=$IMAGEDIR$/logo.png
 Categories=Graphics;2DGraphics;Viewer;
 MimeType=image/bmp;image/gif;image/jpeg;image/jpg;image/pjpeg;image/png;image/tiff;image/x-bmp;image/x-pcx;image/x-png;image/x-portable-anymap;image/x-portable-bitmap;image/x-portable-graymap;image/x-portable-pixmap;image/x-tga;image/x-xbitmap;
 Name[en_US]=feh