[gvfs] Update NEWS for 1.39.91 release

[Ondrej Holy <oholy src gnome org>]

commit 276891b70028ea97fe18c060a4b628c881ed85b0
Author: Ondrej Holy <oholy redhat com>
Date:   Mon Feb 18 15:51:06 2019 +0100

    Update NEWS for 1.39.91 release

 NEWS | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/NEWS b/NEWS
index 084331b3..bf249dd7 100644
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,9 @@
+Major changes in 1.39.91
+========================
+* smb: Do not show password prompt when using winbind ccache
+* Several smaller bugfixes
+* Translation updates
+
 Major changes in 1.39.90
 ========================
 * sftp: Always use port 22 if not specified