Fix GLib notification
The example GLib code from the README fails with
Traceback (most recent call last):
File "/tmp/desktop_notify_test.py", line 6, in <module>
notify = desktop_notify.glib.Notify("summary", "body")
TypeError: Server.__init__() takes 2 positional arguments but 3 were given
because desktop_notify.glib.Notify
has the wrong base class.