code: async function addIncludesToFile(file,
      opt_options) {
    const overrideMap = await readComponentsMap('./amp-versions.json');
    const html = file.contents.toString();
    const newHtml = await addIncludesToHtml(html, overrideMap, opt_options);
    file.contents = new Buffer(newHtml);
    return file;
  }
docs: Identifies missing AMP custom-elementscript tags in an AMP HTML file and
  adds them.
  
  @param {!Vinyl} file The file to add script tags to.
  @param {Object} opt_options See {@code create}.
  @return {!Vinyl} The modified file.