Update PDF.js

To update PDF.js:

1. Go to https://github.com/mozilla/pdf.js/releases/latest and download the pdfjs-<VERSION>-dist.zip file.

2. Remove the old files:

   git rm -r asset/vendor/pdf.js
   

3. Extract the .zip file contents inside asset/vendor/pdf.js:

   unzip pdfjs-<VERSION>-dist.zip -d asset/vendor/pdf.js
   

4. Edit asset/vendor/pdf.js/web/viewer.js and add window.location.origin to HOSTED_VIEWER_ORIGINS. It should look like this:

   const HOSTED_VIEWER_ORIGINS = ["null", "http://mozilla.github.io", "https://mozilla.github.io", window.location.origin];
   

5. Commit!

   git add asset/vendor/pdf.js && git commit -m 'Update PDF.js to <VERSION>'