libubox: update to latest git HEAD

1c08e80 jshn: properly support JSON "null" type

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

package/libs/libubox/Makefile

@@ -4,7 +4,7 @@ PKG_NAME:=libubox
 PKG_RELEASE=1
 
 PKG_SOURCE_PROTO:=git
-PKG_SOURCE_URL=$(LEDE_GIT)/project/libubox.git
+PKG_SOURCE_URL=$(PROJECT_GIT)/project/libubox.git
 PKG_SOURCE_DATE:=2017-10-06
 PKG_SOURCE_VERSION:=729f47fd5279f902986457682f8f166c324eafb5
 PKG_MIRROR_HASH:=5ca03294498f347f437236aeb1d55747264229a46a5ddba93caeb6b3fb735e10