[TimePicker] Update the Adjustement

[Corentin Noël]

The Gtk.Adjustement is not updated when the value time is updated.

replace:

void on_time_changed () {
            text = time.format (format);
        }

by:

void on_time_changed () {
            text = time.format (format);
            int new_time = time.get_hour () * 60 + 30;
            adjustment.set_value (new_time);
        }