js: Use generic actor properties to align StBin children

StBin's fill/align properties are now no-ops; get back the intended
child allocation by setting the corresponding x/y-align on the child.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/803

js/ui/overview.js

@@ -111,7 +111,7 @@ class OverviewActor extends St.BoxLayout {
         this._searchEntry.set_offscreen_redirect(Clutter.OffscreenRedirect.ALWAYS);
         let searchEntryBin = new St.Bin({
             child: this._searchEntry,
-            x_align: St.Align.MIDDLE
+            x_align: Clutter.ActorAlign.CENTER,
         });
         this.add_actor(searchEntryBin);