cmake: upgrade libuv 0.11.26 -> 0.11.27

Adds new `uv_fs_mkdtemp` function which we need for cross-platform temp
directory creation.

ref:
- neovim#812
- joyent/libuv#1368
- https://github.com/joyent/libuv/releases

third-party/CMakeLists.txt

@@ -46,8 +46,8 @@ endif()
 
 include(ExternalProject)
 
-set(LIBUV_URL https://github.com/joyent/libuv/archive/v0.11.26.tar.gz)
-set(LIBUV_MD5 05fabe884173f422649fbe1047ca62b1)
+set(LIBUV_URL https://github.com/joyent/libuv/archive/v0.11.27.tar.gz)
+set(LIBUV_MD5 a557ee3ec3530d9fc1e6ced081574ef8)
 
 set(MSGPACK_URL https://github.com/msgpack/msgpack-c/releases/download/cpp-0.5.8/msgpack-0.5.8.tar.gz)
 set(MSGPACK_MD5 ea0bee0939d2980c0df91f0e4843ccc4)