[gtksourceviewmm] Update NEWS

[Murray Cumming <murrayc src gnome org>]

commit 3928492d12d2d594053773fd4808332cf467d9a2
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Apr 29 13:47:48 2015 +0200

    Update NEWS

 NEWS |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)
---
diff --git a/NEWS b/NEWS
index f2de556..b5401e7 100644
--- a/NEWS
+++ b/NEWS
@@ -1,4 +1,11 @@
-3.12.0:
+3.12.0 (stable):
+
+* Deprecated some API because some of the C API was deprecated.
+  (Murray Cumming)
+* Fix the examples build with recent gtkmm versions.
+  (Murray Cumming)
+
+3.2.0 (stable):
 * Wrapped gtk_source_gutter_get_renderer_at_pos()
   as Gsv::Gutter::get_renderer_at_pos().
   (Krzesimir Nowak)