gif export is not supported by wxWidgets

This 'fixes' #18 by just removing the option to export .gif files

src/gui/set/window.cpp

@@ -549,7 +549,7 @@ void SetWindow::onFileExportImage(wxCommandEvent&) {
 	CardP card = current_panel->selectedCard();
 	if (!card)  return; // no card selected
 	String name = wxFileSelector(_TITLE_("save image"), settings.default_export_dir, clean_filename(card->identification()), _(""),
-		                         _("JPEG images (*.jpg)|*.jpg|Windows bitmaps (*.bmp)|*.bmp|PNG images (*.png)|*.png|GIF images (*.gif)|*.gif|TIFF images (*.tif)|*.tif"),
+		                         _("JPEG images (*.jpg)|*.jpg|Windows bitmaps (*.bmp)|*.bmp|PNG images (*.png)|*.png|TIFF images (*.tif)|*.tif"),
 		                         wxSAVE | wxOVERWRITE_PROMPT, this);
 	if (!name.empty()) {
 		settings.default_export_dir = wxPathOnly(name);