Fixed the `x/y/z plot` script args error.

[Littleor]

The x/y/z plot script have a new args format, so the example in README.md is out of date. This change has led to the emergence of an error message:

list indices must be integers or slices, not str

For further information, please consult the following link: https://github.com/AUTOMATIC1111/stable-diffusion-webui/issues/11736