Minor fixes to docs

[mdtanker]

When reading through the docs I noticed a few small errors which I've fix here.

1. The sphinx cross-referencing to the dask delayed function (:func:dask.delayed) was not properly working throughout the docs. It looks like the proper reference for it is :func:dask.delayed.delayed. I've updated all these cross-references.

2. In the typehints of the docstrings the use of an oxford comma seems to result in "or" being treated as an object instead of text; see the docstrings for the scoring parameter of SplineCV for an example. I've removed the oxford comma for a few docstrings that had them.

I built the docs locally and the changes seem to have worked.

[santisoler]

Nice catches @mdtanker! I'm merging this 🚀

[santisoler]

Squash and Merge summary

Fix cross-references to dask.delayed.delayed. Remove Oxford comma before "or" when listing possible types for arguments. It made the "or" word to be treated as a possible type instead of the connector.