message: (docs) - fix file upload exchange example
  add missing "variables." prefix to path map entries
diff: @@ -480,7 +480,7 @@ if (isFileUpload) {
  const map = {}
  let i = 0
  files.forEach(paths => {
  - map[++i] = paths
  + map[++i] = paths.map(path => `variables.${path}`)
  });
  fetchOptions.body.append('map', JSON.stringify(map));
  