code: function expandMapping(config, options) {
    var len = config.files.length, i = -1;
    var res = [];
  
    while (++i < len) {
      var raw = config.files[i];
      var node = new RawNode(raw, config, this);
      this.emit('files', 'rawNode', node);
      this.emit('rawNode', node);
      if (node.files.length) {
        res.push.apply(res, node.files);
      }
    }
    config.files = res;
    return config;
  }
docs: Iterate over a files array and expand src-dest mappings
  
  ```js
  { files: [ { src: [ '*.js' ], dest: 'dist/' } ] }
  ```
  @param {Object} `config`
  @param {Object} `options`
  @return {Object}