cleanup: Require "dangling" commas

Since ES5, trailing commas in arrays and object literals are valid.
We generally haven't used them so far, but they are actually a good
idea, as they make additions and removals in diffs much cleaner.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/805

js/ui/status/volume.js

@@ -263,7 +263,7 @@ var InputStreamSlider = class extends StreamSlider {
             // as recording because they show the input level
             let skippedApps = [
                 'org.gnome.VolumeControl',
-                'org.PulseAudio.pavucontrol'
+                'org.PulseAudio.pavucontrol',
             ];
 
             showInput = this._control.get_source_outputs().some(output => {