Use goldmark-mathjax extension

@ju52 Did you read the first of this thread?

OK, I will describe the problem here again. The problem of this thread is a conflict between the Markdown spec and the MathJax spec.

When we write the next TeX document in a Markdown file.

$$
\begin{vmatrix}a & b\\
c & d
\end{vmatrix}
$$

Hugo processes the input with the goldmark (CommonMark) and we will get the following HTML output.

<p>$$
\begin{vmatrix}a &amp; b \<br>
c &amp; d
\end{vmatrix}
$$</p>

Since MathJax cannot process the <br> tag, the math rendering is broken.