Support directory removal

[dawsbot]

Currently, you're met with the following error (this is a skrub-cli call, but it makes no difference since it's an issue in this api)

$ skrub <directory>
events.js:141
      throw er; // Unhandled 'error' event
      ^

Error: EISDIR: illegal operation on a directory, open '/Users/dawsonbotsford/<directory>'
    at Error (native)

(directory name redacted)