The diff command on the mac system is overridden by this line of code

https://github.com/ohmyzsh/ohmyzsh/blob/3e7ef0182f59c7990a52cf6ec2981adb56d5b368/lib/theme-and-appearance.zsh#L18

If i write PATH like this 
```shell
EXPORT PATH='xxxx:$PATH'
```
the system `diff` command will be overwrite by this line of code.