cleanup: Use object shorthand where possible

ES6 allows to omit property names where they match the name of the
assigned variable, which makes code less redunant and thus cleaner.
We will soon enforce that in our eslint rules, so make sure we use
the shorthand wherever possible.

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

js/extensionPrefs/main.js

@@ -126,7 +126,7 @@ class Application extends Gtk.Application {
 
         let buffer = new Gtk.TextBuffer({ text: errortext });
         let textview = new Gtk.TextView({
-            buffer: buffer,
+            buffer,
             wrap_mode: Gtk.WrapMode.WORD,
             monospace: true,
             editable: false,