update docstring of TopKCategoricalAccuracy

[btel]

It's a simple edit that replaces capital K with k, which is more consistent with the parameter names of the metrics classes.

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[btel]

@googlebot rescan

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[rthadur]

We will not be encouraging one liner grammatical changes as this is expensive process, thank you for your interest.
CC @mihaimaruseac

[btel]

@rthadur Thank you for your consideration and your time. Although I understand your point, I still do believe that small incremental changes in the documentation might improve developer experience.

[mihaimaruseac]

Every PR takes around 16 CPU/GPU hours of CI. As such, we cannot just run every PR through the CI infrastructure.

If you want to make documentation changes, please pick an entire file and clean it up from end to end, not just a letter here and there.

[btel]

Thank you, @mihaimaruseac, for the explanation. I was put off by the tone of the initial copy-and-paste comment, but of course computational cost should be keept in mind. I would recommend updating the "Contributing guideline" to make the point clear for future contributors.