MathJax formula can't be rendered offline

[njman]

Hi,
I git clone the repository to local machine, open it locally and found that MathJax formula can't be rendered. For example, notation.html include Equation 1. The Discrete Fourier Transform1

$$ \mathrm{DFT}[k] = \sum_{n=0}^{N-1} \mathrm{x}[n] \cdot e^{-\varphi\mathrm{i}} \\ where \quad \varphi = k \frac{n}{N} 2\pi $$

thanks