function md5(bytes) {
  if (Array.isArray(bytes)) {
    bytes = Buffer.from(bytes);
  } else if (typeof bytes === 'string') {
    bytes = Buffer.from(bytes, 'utf8');
  }

  return _crypto.default.createHash('md5').update(bytes).digest();
}
Append a field to a vary header.

@param {String} header
@param {String|Array} field
@return {String}
@public