Fix deprecated warnings with python3-gobject 3.13.3.

python3-gobject adds several warnings in gi/overrides/Gtk.py

/usr/share/ibus/setup/main.py:74: PyGIDeprecationWarning:
Using positional arguments with the GObject constructor has been
deprecated. Please specify keyword(s) for "schema" or use a class
specific constructor.
See: https://wiki.gnome.org/PyGObject/InitializerDeprecations

/usr/share/ibus/setup/main.py:364: PyGTKDeprecationWarning:
The keyword(s) "type" have been deprecated in favor of "message_type"
respectively.
See: https://wiki.gnome.org/PyGObject/InitializerDeprecations

TEST=setup

Review URL: https://codereview.appspot.com/110990044