uv: Upgrade to v0.11.21
src: update to latest libuv api

libuv gyp builds now require you to define the library disposition
(static or shared).

Also, libuv now supports vectored IO for file system reads and writes,
update to those function signatures
src: spawn_sync should close handles upon exit

When the exit callback is fired for the child process we should close
the handle associated with it.