docs: function recurseSrcDirectories (grunt, fileData, options) {
      let promises = [];
  
      // Ignore everything except directories and Javascript files.
      // Store function in array for recursive-readdir module.
      let ignoreCallback = [(file, stats) => !(stats.isDirectory() || path.extname(file) === '.js')];
  
      for (let i = 0, max = fileData.src.length; i < max; i++) {
          promises.push(readDir(fileData.src[i], ignoreCallback).then((value) => value, (err) => err));
      }
  
      Promise.all(promises)
          .then((values) => {
              streamMatches(grunt, fileData, options, values, values.flat());
          }, throwAsyncError);
  }