Update causalgraphicalmodels

[kvaky]

The default causalgraphicalmodels version is not compatible with python 3.9+ (issue). The updated version is compatible with python 3.9+

[fehiepsi]

Thanks, @kvaky! I think it is better to remove the dependency on causalgraphicalmodels. It looks to me that only the Code 6.19 is using it.

Do you think that we can do it with the utilities, like get_model_relations?

[fehiepsi]

By the way, the tests are failing because sample_shape is a keyword argument in guide.sample_posterior(...). Do you want to apply the fix to those guide.sample_posterior calls?

[fehiepsi]

On a second thought, it seems to me that this could be tricky to use the utility. Let me handle this issue instead. Thanks for pointing it out!

[fehiepsi]

I switched to networkx at #31 . Hopefully, it's a more stable solution.

It's quite tricky to get the correct implementation for four variable relations in a causal graph.