php: security bump to version 5.5.15

Fixes:
CVE-2014-4670 (SPL Iterators use-after-free)

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

package/php/php.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-PHP_VERSION = 5.5.14
+PHP_VERSION = 5.5.15
 PHP_SITE = http://www.php.net/distributions
 PHP_INSTALL_STAGING = YES
 PHP_INSTALL_STAGING_OPT = INSTALL_ROOT=$(STAGING_DIR) install