[gtksourceview] NEWS file: add dates for the last two releases

[Sébastien Wilmet <swilmet src gnome org>]

commit 0fdbdfb7d669f2726a9de548fcdeffcd68f5c0a1
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Wed Nov 8 15:04:07 2017 +0100

    NEWS file: add dates for the last two releases
    
    It's what I do in other projects, I think it's useful.

 NEWS |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/NEWS b/NEWS
index b93d882..d99c375 100644
--- a/NEWS
+++ b/NEWS
@@ -1,5 +1,5 @@
-News in 3.99.6
---------------
+News in 3.99.6, 2017-10-15
+--------------------------
 * Reduce a lot the number of translatable strings (especially in *.lang files),
   to translate only what makes sense. 630 -> 93 translatable strings!
 * Build: remove ENABLE_NLS option, always support gettext translation, to
@@ -13,8 +13,8 @@ News in 3.99.6
 * Various other small improvements.
 * Translation updates.
 
-News in 3.99.5
---------------
+News in 3.99.5, 2017-09-06
+--------------------------
 * Avoid type redefinitions.
 * Fix bug when GtkSourceView:indent-width and :tab-width are equal.
 * New syntax highlighting definition file for: Swift, Maxima and Kotlin.