[glibmm] C++11: Glib::Error::what(): Use the override keyword.

[Murray Cumming <murrayc src gnome org>]

commit d614fb94d6c522061d38478251faf2951d8c09f8
Author: Murray Cumming <murrayc murrayc com>
Date:   Mon Oct 26 22:03:59 2015 +0100

    C++11: Glib::Error::what(): Use the override keyword.

 glib/glibmm/error.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/glib/glibmm/error.h b/glib/glibmm/error.h
index 1886d9a..c9758ab 100644
--- a/glib/glibmm/error.h
+++ b/glib/glibmm/error.h
@@ -42,7 +42,7 @@ public:
 
   GQuark domain() const;
   int code() const;
-  virtual Glib::ustring what() const;
+  Glib::ustring what() const override;
 
   bool matches(GQuark error_domain, int error_code) const;