apps-menu: Update menu arrow to use an icon

gnome-shell no longer uses labels with UTF8 arrows, so the currently
used arrow is no longer consistent with other menus; fix that.

https://bugzilla.gnome.org/show_bug.cgi?id=740725

extensions/apps-menu/extension.js

@@ -283,9 +283,7 @@ const ApplicationsButton = new Lang.Class({
                                      y_expand: true,
                                      y_align: Clutter.ActorAlign.CENTER });
         hbox.add_child(this._label);
-        hbox.add_child(new St.Label({ text: '\u25BE',
-                                      y_expand: true,
-                                      y_align: Clutter.ActorAlign.CENTER }));
+        hbox.add_child(PopupMenu.arrowIcon(St.Side.BOTTOM));
 
         this.actor.add_actor(hbox);
         this.actor.name = 'panelApplications';