Add missing API call #229

src/index.js

 import getUUID from './utils/uuid'
 import base64 from 'base-64'
 import polyfill from './polyfill'
+import _ from 'lodash'
 import android from './android'
 import ios from './ios'
 import net from './net'
 
   // # 241 normalize null or undefined headers, in case nil or null string
   // pass to native context
-  headers = _.map(headers, (h) =>  h || '');
+  _.each(headers, (h,i) =>  {
+    headers[i] = h || ''
+  });
 
   // fetch from file system
   if(URIUtil.isFileURI(url)) {

src/ios.js

 
 export default {
   openDocument,
-  previewDocument
+  previewDocument,
+  excludeFromBackupKey
 }