code: function tryWatch(target, callback) {
    if (!target) {
      return logger.halt('invalid watch target')
    }
    if (!callback || typeof callback !== 'function') {
      return logger.halt('invalid watch callback')
    }
  
    return fs.watch(
      target, { persistent: true, recursive: true},
      function (e, file) {
        // todo: exact watch
        callback(e, file)
      }
    )
  }
docs: try to watch with custom callback
  
  @param  {String} target
  @param  {Function} callback
  @return {Object} fs.Watcher