Update jsDelivr links

[LukasDrgon]

jsDelivr switched to a fully automated system, that can serve files from npm and GitHub. This means all future releases will be available automatically, but will use a new link structure.

I updated the links now so you don't forget to do it when you release a new version.

You can find links for all files at https://www.jsdelivr.com/package/npm/codemirror-spell-checker.

I also set the default file to dist/spellchecker.min.js.

Feel free to ping me if you have any questions regarding this change.