libubox: update to the latest version

adds a SIGCHLD handling fix and jshn performance improvements

Signed-off-by: Felix Fietkau <nbd@nbd.name>

package/libs/libubox/Makefile

@@ -1,13 +1,13 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=libubox
-PKG_VERSION:=2016-02-26
+PKG_VERSION:=2016-05-19
 PKG_RELEASE=$(PKG_SOURCE_VERSION)
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL=$(OPENWRT_GIT)/project/libubox.git
 PKG_SOURCE_SUBDIR:=$(PKG_NAME)-$(PKG_VERSION)
-PKG_SOURCE_VERSION:=5326ce1046425154ab715387949728cfb09f4083
+PKG_SOURCE_VERSION:=1257a38a6e64511207bb3b077ca7e8e1a3338fc1
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION)-$(PKG_SOURCE_VERSION).tar.gz
 PKG_MIRROR_MD5SUM:=
 CMAKE_INSTALL:=1