math/rand/v2: replace <= 0 with == 0 for Uint function docs
This harmonize the docs with (*Rand).Uint* functions.
And it make it clearer, I wasn't sure if it would try to interpret
the uint as a signed number somehow, it does not pull any surprises
make that clear.
Change-Id: I5a87a0a5563dbabfc31e536e40ee69b11f5cb6cf
Reviewed-on: https://go-review.googlesource.com/c/go/+/633535
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Commit-Queue: Ian Lance Taylor <iant@google.com> Reviewed-by: Ian Lance Taylor <iant@google.com>
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