mosquitto: bump to version 1.6.8

This is a bugfix release.
Full changelog available at:
https://mosquitto.org/blog/2019/11/version-1-6-8-released/

Many smaller fixes in various areas, nothing particularly standout as of
special interest to OpenWrt.

Signed-off-by: Karl Palsson <karlp@etactica.com>

net/mosquitto/Makefile

@@ -9,7 +9,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=mosquitto
-PKG_VERSION:=1.6.7
+PKG_VERSION:=1.6.8
 PKG_RELEASE:=1
 PKG_LICENSE:=BSD-3-Clause
 PKG_LICENSE_FILES:=LICENSE.txt
@@ -17,7 +17,7 @@ PKG_CPE_ID:=cpe:/a:eclipse:mosquitto
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=https://mosquitto.org/files/source/
-PKG_HASH:=bcd31a8fbbd053fee328986fadd8666d3058357ded56b9782f7d4f19931d178e
+PKG_HASH:=7df23c81ca37f0e070574fe74414403cf25183016433d07add6134366fb45df6
 
 include $(INCLUDE_DIR)/package.mk