Use jsdelivr as a CDN to fix broken links

[davepagurek]

In #3457 we noticed that some CDN links were broken, and changed the version back to 1.11.3.

It seems that this is a cloudflare CDN issue, with them not updating especially quickly when we release a new version. In the past we switched to jsdelivr as our CDN on the p5.js website as they seem to update much more quickly. I had started using jsdelivr URLs in the version picker here too, but only when you start to change the version -- the default was using Cloudflare as before. So a possible solution is to just use jsdelivr as the default.

Changes:

• Bumps default version back to 1.11.5
• Makes the initial sketch use jsdelivr instead of cloudflare cdnjs
  • We still detect cloudflare CDN links, we just don't use them when you switch versions

The p5 version in the default sketch seems to work now!

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123

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[raclim]

Thanks for confirming and updating the links, I'll push this out!