Use jsDelivr instead of the GitHub API for content

[whymarrh]

Refs #219

At the request of GitHub, this change updates how we query for the latest blocklist content. We now hit jsDelivr instead of the GitHub API.

[Gudahtt]

LGTM!

[whymarrh]

Note their Acceptable Use Policy.

I think esp. with #257 that we aren't in violation of their policy:

✅ Any content accessed via jsDelivr must conform to the terms of the service from which it was retrieved
✅ As long as you do not violate our rules [...] there are no limits on bandwidth or number of requests
✅ We don't exceed any of their hard limits
✅ For projects using our GitHub proxy [...] the number of actively accessed files per repository does not exceed 10,000

Their listed prohibited uses:

2. Abusing the service and its resources, or using jsDelivr as a general-purpose
   file or media hosting service. This includes, for example:

   • running an image hosting website and using jsDelivr as a storage for all
     uploaded images,
   • hosting videos, file backups, or other files in large quantities.

   We recognize that there are legitimate projects that consist of a large number
   of files, and these are not considered abuse. For example: icons packs, apps,
   or games with a large number of assets.

3. Trying to bypass our limits or restrictions in any way. We will be happy
   to remove limits or provide custom solutions for legitimate projects.

I don't think any of that applies here. This isn't general-purpose file-hosting.