code: function globsToExcludeFromFileSet (dirname, fileset) {
    if (fileset.excludes && fileset.excludes.length) {
      return fileset.excludes.map(exclude => '!' + path.join(dirname, exclude));
    } else {
      return [];
    }
  }
docs: The excludes in a fileset are all treated as globs. This extracts all of
  them and makes them absolute.
  
  @param {!string} dirname
  @param {Array<{excludes: Array<string>}>} fileset
  @returns {Array<string>}