vendor: update pdf.js to v2.1.266 (#7834)

Author: sapk

public/vendor/VERSIONS

@@ -48,7 +48,7 @@ File(s): /vendor/plugins/simplemde/simplemde.min.js
 Version: 1.10.1
 
 File(s): /vendor/plugins/pdfjs/
-Version: 1.4.20
+Version: 2.1.266
 
 File(s): /vendor/plugins/u2f/
 Version: 1.0.8

public/vendor/librejs.html

@@ -108,7 +108,7 @@
         <tr>
           <td><a href="./plugins/pdfjs/">pdf.js</a></td>
           <td><a href="https://github.com/mozilla/pdf.js/blob/master/LICENSE">Apache-2.0-only</a></td>
-          <td><a href="https://github.com/mozilla/pdf.js/archive/v1.4.20.tar.gz">pdf.js-v1.4.20.tar.gz</a></td>
+          <td><a href="https://github.com/mozilla/pdf.js/archive/v2.1.266.tar.gz">pdf.js-v2.1.266.tar.gz</a></td>
         </tr>
 		<tr>
 		  <td><a href="./plugins/u2f/">u2f-api</a></td>