code: function (headers, key, def) {
      if (headers instanceof Array) {
        var regex = new RegExp(key, 'i')
        for (var i = 0; i < headers.length; i++) {
          if (regex.test(headers[i].name)) {
            return headers[i].value
          }
        }
      }
  
      return def !== undefined ? def : false
    }
docs: uses regex to match a header value