Gtk.SpinButton.new_with_range is not a constructor
Gtk.SpinButton.new_with_range is not a constructor

It's just a function that returns the new spin button so it should not be used
with the "new" statement.

It's strange tough that this worked fine for both gnome shell 3.4 and 3.8.

fixes #13

hackedbellini/gnome-shell-notifications-alert