bug report: process cmd error on Linux

## Env
- OS:  Pop!_OS 20.04 LTS(base on Ubuntu 20.04)

 ## Log

[![bQ8YJH.md.png](https://s4.ax1x.com/2022/03/01/bQ8YJH.md.png)](https://imgtu.com/i/bQ8YJH)

## Reason
https://github.com/SummerSec/SPATool/blob/2823aef4adf0f8c3a9a5dfebb239cc760e6ecea1/src/main/java/com/sumsec/core/ast/util/DotHandler.java#L44

Like windows if branch , replace "+" to "," may fix the bug.