The previous Windows implementation used SHGetKnownFolderPath(),
which is only supported on Vista and up. This commit switches to
GetUserProfileDirectoryW(), which returns the same information,
but is supported back to Windows 2000, and is not deprecated.
PR-URL: https://github.com/libuv/libuv/pull/375
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>