Fix memory leaks in drw

Synced from dwm.
Patch by Alex Flierl <shad0w73@freenet.de>, thanks.

drw.c

@@ -95,6 +95,7 @@ drw_free(Drw *drw)
 {
 	XFreePixmap(drw->dpy, drw->drawable);
 	XFreeGC(drw->dpy, drw->gc);
+	drw_fontset_free(drw->fonts);
 	free(drw);
 }