Add integrity check for remote resource

[davel]

Adds an integrity attribute so that we no longer blindly trust the CDN for pdfobject.min.js. crossorigin is now necessary for the resource to continue to load.

https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity

[HackbrettXXX]

Thanks for the PR. How did you create the hash? cdnjs usually creates sha512 hashs:

<script src="https://cdnjs.cloudflare.com/ajax/libs/pdfobject/2.1.1/pdfobject.min.js" integrity="sha512-4ze/a9/4jqu+tX9dfOqJYSvyYd5M6qum/3HpCLr+/Jqf0whc37VUbkpNGHR7/8pSnCFw47T1fmIpwBV7UySh3g==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>

[davel]

Thanks for the PR. How did you create the hash? cdnjs usually creates sha512 hashs:

<script src="https://cdnjs.cloudflare.com/ajax/libs/pdfobject/2.1.1/pdfobject.min.js" integrity="sha512-4ze/a9/4jqu+tX9dfOqJYSvyYd5M6qum/3HpCLr+/Jqf0whc37VUbkpNGHR7/8pSnCFw47T1fmIpwBV7UySh3g==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>

I have upgraded the hash to sha512.

To generate the hash I followed the suggested commands on the Mozilla link. This should give you the same hash,

curl https://cdnjs.cloudflare.com/ajax/libs/pdfobject/2.1.1/pdfobject.min.js | openssl dgst -sha512 -binary | openssl base64 -A

[HackbrettXXX]

Alright, looks good. Thanks!