Mathematical notations are not rendered

[CyrusYip]

See: https://github.com/CyrusYip/cyrusyip-blog/pull/1#issue-1372663731

Example:

• https://github.com/CyrusYip/cyrusyip-blog/blob/main/content/zh-cn/post/2020-11-28-nobody-in-university.md
• http://localhost:1313/zh-cn/post/2020/11/26/regex-examples/

Todos:

• [ ] enable MathJax
• [ ] replace $..$ with \(...\) because dollar signs appear too often in non-mathematical text.
• [ ] compatible with pandoc https://pandoc.org/MANUAL.html#math

[CyrusYip]

Actually, I don't need mathematical notation.

https://github.com/CyrusYip/cyrusyip-blog/commit/fcc4549f52e26824449015d64bbdb4e3a20c9ed0