fix(KaTeX): Use jsdelivr instead of bootcdn

[tomodachi94]

Bootcdn was compromised by a malicious actor: https://sansec.io/research/polyfill-supply-chain-attack

KaTeX recommends using jsdelivr, so I used that: https://katex.org/docs/browser

[pylixm]

这是来自QQ邮箱的假期自动回复邮件。您好，我最近正在休假中，无法亲自回复您的邮件。我将在假期结束后，尽快给您回复。

[pylixm]

Thank you for your commit.