Fresh pip install seems to require matplotlib

```console
❯ overreact model.k
Traceback (most recent call last):
File "/home/schneider/.local/bin/overreact", line 5, in
from overreact._cli import main
File "/home/schneider/.local/lib/python3.9/site-packages/overreact/_cli.py", line 15, in
import matplotlib.pyplot as plt
ModuleNotFoundError: No module named 'matplotlib'
```

The offending line is the following:

https://github.com/geem-lab/overreact/blob/ee548e40f20ad472d0958f2d86f5ff80f7079ccf/overreact/_cli.py#L15