code: function (callback) {
  					const str = files[file].contents.toString();
  					if (!handlebarsMatcher.test(str)) {
  						return callback();
  					}
  
  					render(str, metadata, function (err, res) {
  						if (err) return callback(err);
  						files[file].contents = Buffer.from(res);
  						callback();
  					});
  				}
docs: interpolate the file contents