[gtkmm-documentation] Update NEWS for next release.

[Murray Cumming <murrayc src gnome org>]

commit d32f91f9cae290925fc83b5d7847e4c2c1be5ad0
Author: Murray Cumming <murrayc murrayc com>
Date:   Mon Aug 24 00:02:31 2015 +0200

    Update NEWS for next release.
    
    To mention a commit that got in before I remembered to push the
    release commit (again).

 NEWS |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/NEWS b/NEWS
index 016fa46..99b55fb 100644
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,7 @@
+
+* Replace deprecated std::auto_ptr by std::unique_ptr.
+  (Kjell Ahlstedt)
+
 3.17.50 (unstable):
 
 * Use (and require) C++11.