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/userWidget.js

@@ -26,7 +26,7 @@ class Avatar extends St.Bin {
             style_class: params.styleClass,
             reactive: params.reactive,
             width: params.iconSize * themeContext.scaleFactor,
-            height: params.iconSize * themeContext.scaleFactor
+            height: params.iconSize * themeContext.scaleFactor,
         });
 
         this._iconSize = params.iconSize;