Fix FormData usage in karma tests

spec/javascripts/blob/blob_file_dropzone_spec.js

@@ -24,10 +24,7 @@ describe('BlobFileDropzone', function() {
     it('is disabled while uploading', () => {
       spyOn(window, 'alert');
-      const file = {
-        name: 'some-file.jpg',
-        type: 'jpg',
-      };
+      const file = new File([], 'some-file.jpg');
       const fakeEvent = $.Event('drop', {
         dataTransfer: { files: [file] },
       });

spec/javascripts/dropzone_input_spec.js

@@ -2,9 +2,9 @@ import $ from 'jquery';
 import dropzoneInput from '~/dropzone_input';
 import { TEST_HOST } from 'spec/test_constants';
-const TEST_FILE = {
-  upload: {},
-};
+const TEST_FILE = new File([], 'somefile.jpg');
+TEST_FILE.upload = {};
+
 const TEST_UPLOAD_PATH = `${TEST_HOST}/upload/file`;
 const TEST_ERROR_MESSAGE = 'A big error occurred!';
 const TEMPLATE = `<form class="gfm-form" data-uploads-path="${TEST_UPLOAD_PATH}">