add pydantic as a dependency

[rasca]

In a clean install when trying to use kerykeion I get:

File ".../lib/python3.9/site-packages/kerykeion/types.py", line 9, in <module>
    from pydantic import BaseModel
ModuleNotFoundError: No module named 'pydantic'

[g-battaglia]

Ok thanks, I updated the dependencies, now it should work! Let me know if it's ok also on your machine!