uv: upgrade to v0.11.10
process_wrap: don't coerce process exit code to int32_t

On windows process exit codes can be greater than INT32_MAX. This used
to be not much of a problem - greater values would just come out
negative. However since ca9eb71 a negative result value indicates that
uv_spawn() has failed, so this is no longer acceptable.
src: remove pointless node_os.h header file

src/node_os.cc doesn't export anything that's used elsewhere. Remove it.