php: security bump to version 5.6.20

Fixes (no CVEs yet):
Buffer over-write in finfo_open with malformed magic file.
Invalid memory write in phar on filename with \0 in name.
Parsing of tar file with duplicate filenames causes memory leak.
php_snmp_error() Format String Vulnerability.
Integer Overflow in php_raw_url_encode.

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
-sha256	bb32337f93a00b71789f116bddafa8848139120e7fb6f4f98a84f52dbcb8329f	php-5.6.19.tar.xz
+sha256	2b87d40213361112af49157a435e0d4cdfd334c9b7c731c8b844932b1f444e7a	php-5.6.20.tar.xz

package/php/php.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-PHP_VERSION = 5.6.19
+PHP_VERSION = 5.6.20
 PHP_SITE = http://www.php.net/distributions
 PHP_SOURCE = php-$(PHP_VERSION).tar.xz
 PHP_INSTALL_STAGING = YES