Fix another rtd bug

[hpesonen]

Summary:

Changed readthedocs configuration files as they were becoming deprecated.

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[uremes]

oh i realised the changelog is not updated. maybe not important but here is a reminder in case it should be

[hpesonen]

oh i realised the changelog is not updated. maybe not important but here is a reminder in case it should be

Oh, good, point. It wasn't updated because everything was related to rtd config before. but now the PR has spilled to other parts as well. at minimum I'll add the pinning of numpy to changelog as a separate note