bump version, update NEWS

NEWS

+Knot DNS 1.6.8 (2016-08-09)
+===========================
+
+Features:
+ - Zone size limit restriction for DDNS, AXFR, and IXFR (CVE-2016-6171)
+
 Knot DNS 1.6.7 (2016-02-08)
 ===========================
 
 Improvements:
 -------------
-- IXFR: Log change of the zone serial number after the transfer
-- RRL: Document operational impact of various settings
-- RRL: Add support for zero slip (dropping of all limited responses)
-- Added 'timer-db' configuration option allowing relocation of timer database
+ - IXFR: Log change of the zone serial number after the transfer
+ - RRL: Document operational impact of various settings
+ - RRL: Add support for zero slip (dropping of all limited responses)
+ - Added 'timer-db' configuration option allowing relocation of timer database
 
 Knot DNS 1.6.6 (2015-11-24)
 ===========================

configure.ac

 #                                               -*- Autoconf -*-
 
 AC_PREREQ([2.60])
-AC_INIT([knot], [1.6.7], [knot-dns@labs.nic.cz])
+AC_INIT([knot], [1.6.8], [knot-dns@labs.nic.cz])
 AM_INIT_AUTOMAKE([gnits subdir-objects dist-xz -Wall -Werror])
 AM_SILENT_RULES([yes])
 AC_CONFIG_SRCDIR([src/knot/main.c])