libubox: update to the latest version

Adds the following changes:

de3f14b uloop: add uloop_cancelling function
3b6181b utils: fix build on Mac OS X 10.12
7f671b1 blobmsg: add support for double
0fe1374 utils: add helper functions useful for allocating a ring buffer
8fc1c30 libubox: replace strtok with _r version.
4a9f74f libubox: allow reading out the pid of uloop process in lua
372e1e6 uloop: remove useless epoll data assignment
f9db1cb libubox: allow reading out the remaining time of a uloop timer in Lua

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