title: firebase function with formidable has the file object undefined
body: <pre><code> exports.storePostData = functions.https.onRequest(function (request, 
  response) {
  cors(request, response, function () {
  var uuid = UUID();
  var formData = new formidable.IncomingForm();
  
  formData.parse(request, function(err, fields, files) {
  
    fs.rename(files.file.path, '/tmp/' + files.file.name);
    var bucket = gcs.bucket('pwagram-87530.appspot.com');
  
    bucket.upload('/tmp/' + files.file.name, {
      uploadType: 'media',
      metadata: {
        metadata: {
          contentType: files.file.type,
          firebaseStorageDownloadTokens: uuid
        }
      }
    }, function(err, file) {
  
      if (!err) {
        admin.database().ref('posts').push({
          id: fields.id,
          title: fields.title,
          location: fields.location,
          rawLocation: {
            lat: fields.rawLocationLat,
            lng: fields.rawLocationLng
          },
          image: 'https://firebasestorage.googleapis.com/v0/b/' + bucket.name 
          + '/o/' + encodeURIComponent(file.name) + '?alt=media&amp;token=' + uuid
        })
  </code></pre>
  
  <p>the function log is throwing the error "cannot read property path of 
  undefined", which i guess is from the fact that the formidable files object 
  is empty..will appreciate if anyone could help. i can't seem to figure out what i'm doing wrong.</p>