code: function watch(path, cb) {
      debug('watching %s for changes', path);
  
      var options = {ignoreInitial: true, persistent: true},
          watcher = chokidar.watch(path, options);
  
      watcher.on('change', function(path, stat) {
  
        /* istanbul ignore next */
        debug(format("%s changed", path));
  
        /* istanbul ignore next */
        cb.call(this, path, stat);
  
      }.bind(this));
  
      return watcher;
    }
docs: setup a chokidar persistent watcher on a dir or file and call
  the callback on `change` event
  
  @param  {String}   path directory (recursive) or file path to watch
  @param  {Function} cb   callback to call on `change` event
  @return {choikdar.watcher}        the watcher instance created