desktop/xfce4-mailwatch-plugin: Update doinst.sh.

Signed-off-by: Willy Sudiarto Raharjo <willysr@slackbuilds.org>

desktop/xfce4-mailwatch-plugin/doinst.sh

@@ -1,5 +1,5 @@
 if [ -e usr/share/icons/hicolor/icon-theme.cache ]; then
   if [ -x /usr/bin/gtk-update-icon-cache ]; then
-    /usr/bin/gtk-update-icon-cache usr/share/icons/hicolor >/dev/null 2>&1
+    /usr/bin/gtk-update-icon-cache -f usr/share/icons/hicolor >/dev/null 2>&1
   fi
 fi