iconGrid: Chain up in style-changed

Commit 81ec8215a0 moved the handling of style changes from a signal
handler to a vfunc without chaining up to the parent, losing propagating
the change to children and queueing a paint update.

https://gitlab.gnome.org/GNOME/gnome-shell/issues/1117

js/ui/iconGrid.js

@@ -104,6 +104,7 @@ class BaseIcon extends St.Bin {
     }
 
     vfunc_style_changed() {
+        super.vfunc_style_changed();
         let node = this.get_theme_node();
 
         let size;