php: security bump to version 5.5.18

Fixes:
CVE-2014-3669 - Integer overflow in unserialize() (32-bits only)
CVE-2014-3670 - Heap corruption in exif_thumbnail()
CVE-2014-3668 - Global buffer overflow in mkgmtime() function

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Acked-by: Bernd Kuhls <bernd.kuhls@t-online.de>
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	e5f25dae73004658533ee7701a527bd0	php-5.5.17.tar.xz
+md5	3984f32985842afebe5795457e26931f	php-5.5.18.tar.xz

package/php/php.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-PHP_VERSION = 5.5.17
+PHP_VERSION = 5.5.18
 PHP_SITE = http://www.php.net/distributions
 PHP_SOURCE = php-$(PHP_VERSION).tar.xz
 PHP_INSTALL_STAGING = YES