[glibmm] RefPtr: Minor documentation fix

[Kjell Ahlstedt <kjellahl src gnome org>]

commit f35efbbd261810c83f675c032092393c04522061
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Tue Apr 18 20:08:29 2017 +0200

    RefPtr: Minor documentation fix
    
    Gdk::Pixmap does not exist in gtkmm3 or gtkmm4. Don't mention it.

 glib/glibmm/refptr.h |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/glib/glibmm/refptr.h b/glib/glibmm/refptr.h
index 149f9a5..8edf68b 100644
--- a/glib/glibmm/refptr.h
+++ b/glib/glibmm/refptr.h
@@ -73,11 +73,11 @@ make_refptr(T_Arg... arg)
  * unreference() methods, and whose destructor is noexcept (the default for destructors).
  *
  * In gtkmm, that is anything derived from Glib::ObjectBase, such as
- * Gdk::Pixmap.
+ * Gdk::Pixbuf.
  *
  * Normal application code should not need to use this. However, this is necessary
  * when implementing create() methods for derived Glib::ObjectBase-derived
- * (not Gtk::Widget-derived) classes,  such as derived Gtk::TreeModels.
+ * (not Gtk::Widget-derived) classes, such as derived Gtk::TreeModels.
  */
 template <class T_CppObject>
 RefPtr<T_CppObject>