gulpfile.js
function rename(obj) {
  return rename_(function(parsedPath) {
    return {
      extname: obj.extname || parsedPath.extname,
      dirname: (obj.dirnamePrefix || '') + parsedPath.dirname,
      basename: parsedPath.basename
    };
  });
}
function rename(obj) {
  return rename_(function(parsedPath) {
    return {
      extname: obj.extname || parsedPath.extname,
      dirname: (obj.dirnamePrefix || '') + parsedPath.dirname,
      basename: parsedPath.basename
    };
  });
}
A wrapper around gulp-rename to support `dirnamePrefix`.