docs: function fileMapToBuffer(fileMap) {
    return Promise.all(
      Array.from(fileMap.entries()).map(([path, file]) =>
        readArrayBuffer(file).then(buffer => ({ buffer, path }))
      )
    )
      .then(results => {
        const zipFile = new yazl.ZipFile();
        results.forEach(result => {
          zipFile.addBuffer(Buffer.from(result.buffer), result.path);
        });
        zipFile.end();
        return zipFile;
      })
      .then(
        zipFile =>
          new Promise(resolve => {
            const output = new streamBuffers.WritableStreamBuffer();
            output.on("finish", () => {
              resolve(output.getContents());
            });
            zipFile.outputStream.pipe(output);
          })
      );
  }