[libsigcplusplus] weak_raw_ptr: Minor use of auto

[Murray Cumming <murrayc src gnome org>]

commit 54dcd80c12322b04117a94af1bb62e3a84412e1b
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Apr 21 14:55:49 2017 +0200

    weak_raw_ptr: Minor use of auto
    
    Noticed by clang-tidy.

 sigc++/weak_raw_ptr.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/sigc++/weak_raw_ptr.h b/sigc++/weak_raw_ptr.h
index 7d67dbc..ccae1b0 100644
--- a/sigc++/weak_raw_ptr.h
+++ b/sigc++/weak_raw_ptr.h
@@ -92,7 +92,7 @@ private:
    */
   static void notify_object_invalidated(notifiable* data)
   {
-    weak_raw_ptr* self = static_cast<weak_raw_ptr*>(data);
+    auto self = static_cast<weak_raw_ptr*>(data);
     if(!self)
       return;