Pydantic security vulnerability CVE-2021-29510

[Kludex]

Hi there 👋

I'm not sure if this is important for thinc, but I'll mention just in case. Feel free to close it. 😅

Pydantic published a security vulnerability yesterday, which you can check it here.

The way that was handled on FastAPI is to not allow versions that are different from the ones with the security patch, as you can see here.

I guess this is relevant as we don't want to allow a Pydantic version with this security vulnerability as requirement. 😗