code: function rmdirWalk( ls, done ) {
    if( ls.length === 0 ) return done()
    fs.rmdir( ls.shift().path, function( error ) {
      if( error ) log( error.message )
      rmdirWalk( ls, done )
    })
  }
docs: Walk an array of directories and
  delete one after another
  @param {Array<Object>} ls
  @param {Function} done