Error converting .svg into .png

[liuchaobit]

I used mathjax to produce the latex formula,
and I use gitbook serve to produce webpages with correct formulas
however, when I use gitbook pdf to produce a pdf file,
I got

error: error while generating page "chapter1/14-shu-zhi-fang-zhen-shi-li-ff1a-xin-guan-fei-yan-yu-ce.md":

Error: Error converting C:\Users\Administrator\AppData\Local\Temp\tmp-47768poGb4f1fkPK_mathjax_46d8639.svg into C:\Users\Administrator\AppData\Local\Temp\tmp-47768poGb4f1fkPK\c6231af5.png

I check the markdown file, I find only one latex code there,

$$ \begin{array}{c} S[T+1]-S[T]=-r \beta I S / N \\ E[T+1]-E[T]=r \beta I S / N-\alpha E \\ I[T+1]-I[T]=\alpha E-\gamma I \\ R[T+1]-R[T]=\gamma I \end{array} $$