Equation not rendered correctly

Hi,
the vertical and horizontal bars inside the array environment are not displayed. Try this equation:
`A=\left(\begin{array}{cc|cc|c} 3 & 7 & 0 & 1 & 12\\\hline 0 & 9 & 21 & 3 & 8\\ 2 & 1 & 5 & 4 & 0\\ \hline 6 & 13 & 0 & 8 & 9 \end{array}\right)`
and compare the result in https://math.vercel.app/home and https://www.mathjax.org/#demo
Otherwise, a nice and useful piece of code!
Milos
