Update libuv

This update brings a few months of changes, but primarily a fix for the
following situation.

When creating a handle to stdin, libuv used to set the stdin handle to
nonblocking mode. This would end up affect this stdin handle across all
processes that shared it, which mean that stdin become nonblocking for everyone
using the same stdin. On linux, this also affected *stdout* because stdin/stdout
roughly point at the same thing.

This problem became apparent when running the test suite manually on a local
computer. The stdtest suite (running with libgreen) would set stdout to
nonblocking mode (as described above), and then the next test suite would always
fail for a printing failure (because stdout was returning EAGAIN).

This has been fixed upstream, joyent/libuv@342e8c, and this update pulls in this
fix. This also brings us in line with a recently upstreamed libuv patch.

Closes #13336
Closes #13355