Flush the cairo surface after drawing

It is perfectly valid for a cairo surface to delay the actual. This is mostly
done in situations where it speeds stuff up. Since we want our drawing to be
visible, we have to flush the cairo surface when we are done drawing.

Signed-off-by: Uli Schlachter <psychon@znc.in>

widget.c

@@ -343,6 +343,8 @@ widget_render(wibox_t *wibox)
             widgets->tab[i].widget->draw(widgets->tab[i].widget,
                                          ctx, widgets->tab[i].geometry, wibox);
 
+    cairo_surface_flush(ctx->surface);
+
     switch(wibox->orientation)
     {
         case South: