opencv: Update to version 3.1.0

This solves the compiling errors with the musl C library.

Signed-off-by: Luis Araneda <luaraneda@gmail.com>

libs/opencv/Makefile

@@ -1,6 +1,6 @@
 #
 # Copyright (C) 2013-2014 wrtnode.com
-# Copyright (C) 2015 OpenWrt.org
+# Copyright (C) 2015-2016 OpenWrt.org
 #
 # This is free software, licensed under the GNU General Public License v2.
 # See /LICENSE for more information.
@@ -9,12 +9,12 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=opencv
-PKG_VERSION:=3.0.0
+PKG_VERSION:=3.1.0
 PKG_RELEASE:=1
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).zip
 PKG_SOURCE_URL:=http://sourceforge.net/projects/opencvlibrary/files/opencv-unix/$(PKG_VERSION)/
-PKG_MD5SUM:=09004c275d8092cbdf5b61675cecd399
+PKG_MD5SUM:=6082ee2124d4066581a7386972bfd52a
 
 PKG_LICENSE:=BSD-3-Clause
 PKG_LICENSE_FILES:=LICENSE