cleanup: Use arrow notation for anonymous functions

Arrow notation is great, use it consistently through-out the code base
to bind `this` to anonymous functions, replacing the more overbose
Lang.bind(this, function() {}).

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/23

js/ui/panelMenu.js

@@ -214,9 +214,7 @@ var SystemIndicator = new Lang.Class({
     },
 
     _syncIndicatorsVisible() {
-        this.indicators.visible = this.indicators.get_children().some(function(actor) {
-            return actor.visible;
-        });
+        this.indicators.visible = this.indicators.get_children().some(a => a.visible);
     },
 
     _addIndicator() {