code: function getFiles(config) {
  
  	return new Promise((resolve, reject) => {
  
  		const src = config.src;
  		let files = [];
  		let i = 0;
  
  		(function proceed(error, moreFiles) {
  
  			if(error !== null) {
  
  				reject(error);
  
  			} else {
  
  				files = files.concat(moreFiles);
  
  				if(i === src.length) {
  
  					if(files.length === 0) {
  
  						reject("No input files found");
  
  					} else {
  
  						resolve([config, files]);
  
  					}
  
  				} else {
  
  					glob(src[i++], proceed);
  
  				}
  
  			}
  
  		}(null, []));
  
  	});
  
  }
docs: Gathers files that will be modified.
  
  @type {Object} config - A configuration.
  @return {Promise} A promise that returns an array containing the given configuration and the identified files.