Fixed pdf tests

spec/javascripts/pdf/index_spec.js

 import Vue from 'vue';
-import { PDFJS } from 'vendor/pdf';
+import { GlobalWorkerOptions } from 'vendor/pdf';
 import workerSrc from 'vendor/pdf.worker.min';
 
 import PDFLab from '~/pdf/index.vue';
 import pdf from '../fixtures/blob/pdf/test.pdf';
 
-PDFJS.workerSrc = workerSrc;
+GlobalWorkerOptions.workerSrc = workerSrc;
 const Component = Vue.extend(PDFLab);
 
 describe('PDF component', () => {

spec/javascripts/pdf/page_spec.js

@@ -12,7 +12,7 @@ describe('Page component', () => {
   let testPage;
 
   beforeEach(done => {
-    pdfjsLib.PDFJS.workerSrc = workerSrc;
+    pdfjsLib.GlobalWorkerOptions.workerSrc = workerSrc;
     pdfjsLib
       .getDocument(testPDF)
       .then(pdf => pdf.getPage(1))