Tested and fixed on 0.10.33

With this change, tests passed with node 0.10.33.
There's no explanation why this fixes things on node 10 vs 8, but looking at the docs:

http://nodejs.org/api/fs.html#fs_fs_writesync_fd_buffer_offset_length_position

both offset & length are required arguments. Can you please explain what's going on here (with a code comment)?