Switch CDN provider in documentation

[ayuhito]

I think it'd be appropriate for pure to move away from promoting usage of unpkg to an alternative like jsDelivr.

unpkg is unmaintained and full of issues. On the other hand, jsDelivr is actively maintained and offers more reliability due to its fallback system.

I'd be more than happy to make a PR changing all references of unpkg if the team believes it's appropriate to switch.

[redonkulus]

We do mention jsDelivr on the Customize page for combo URLs. I'm fine migrating from unpkg.com to jsDelivr if unpkg is unmaintained.

Do you want to open a PR to migrate the code?

[ayuhito]

Sure thing, I'll be happy to do so in a couple of hours.