[Rd] Typo in ?base::Bessel

[EDUARDO GARCIA PORTUGUES]

"So*c*kne, David J. (1973)." -> "Sookne, David J. (1973)."

"Sookne" is referred previously in the documentation and is the correct
surname in the publication
<https://pdfs.semanticscholar.org/9cdc/c4aa1562200e6fa50b1400909d1355c3e4f0.pdf>
and Netlib's source <https://www.netlib.org/specfun/ribesl>.

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