function doConcat(files, output) {
  return new Promise((resolve, reject) => {
    concat(files, output, (err) => {
      if (err) return reject(err);
      resolve();
    });
  });
}
/*.css'))
      .then(files => doConcat(files.sort(), 'dist/iD.css'))
      .then(() => {
        const css = fs.readFileSync('dist/iD.css', 'utf8');
        return postcss([
            autoprefixer,
            prepend({ prefix: '.ideditor', exclude: [ /^\.ideditor(\[.*?\])