Rename cumulative (typo?)

[Yosuke-Ito-345]

Motivation for this change

It is a small change, but cumulativeNy0 and cumulativey1 in lebesgue_stieltjes_measure.v should be renamed?

Checklist

• added corresponding entries in CHANGELOG_UNRELEASED.md

• added corresponding documentation in the headers

Reference: How to document

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[affeldt-aist]

That makes sense, could you document the change in the changelog also?

[Yosuke-Ito-345]

Thank you for the comment. I will add it.
Also I'm going to modify probability.v...

[Yosuke-Ito-345]

The checks have passed!
It's ready for review.

[Yosuke-Ito-345]

Thank you for the review and the merge.