[gdm] utils: Don't use deprecated gdk_cursor_unref

[Robert Ancell <rancell src gnome org>]

commit a54358a960a77f098c78ad226161b43357190f7b
Author: Robert Ancell <robert ancell canonical com>
Date:   Tue Dec 5 15:20:34 2017 +1300

    utils: Don't use deprecated gdk_cursor_unref

 utils/gdm-screenshot.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/utils/gdm-screenshot.c b/utils/gdm-screenshot.c
index 01b3585..5d20929 100644
--- a/utils/gdm-screenshot.c
+++ b/utils/gdm-screenshot.c
@@ -76,7 +76,7 @@ screenshot_grab_lock (void)
         cursor = gdk_cursor_new_for_display (gdk_display_get_default (), GDK_WATCH);
         gdk_pointer_grab (gtk_widget_get_window (selection_window), FALSE, 0, NULL,
                           cursor, GDK_CURRENT_TIME);
-        gdk_cursor_unref (cursor);
+        g_object_unref (cursor);
 
         result = TRUE;