php: security bump to version 5.6.8

Fixes:
CVE-2015-1351 - OPCache: Use After Free
CVE-2015-1352 - Postgres: Null pointer dereference

And others with no CVE assigned yet.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/php/php.hash

@@ -1,2 +1,2 @@
 # From http://php.net/downloads.php
-md5	4e04eb021de009981ed963f993a171c1	php-5.6.7.tar.xz
+md5	526a5a7f593de632cd9e8546335de8b7	php-5.6.8.tar.xz

package/php/php.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-PHP_VERSION = 5.6.7
+PHP_VERSION = 5.6.8
 PHP_SITE = http://www.php.net/distributions
 PHP_SOURCE = php-$(PHP_VERSION).tar.xz
 PHP_INSTALL_STAGING = YES