docs: add missing reference and use correct citation identifier

Signed-off-by: Athan <kgryte@gmail.com>

Author: kgryte

lib/node_modules/@stdlib/stats/base/ndarray/dnanmeanwd/README.md

@@ -123,7 +123,8 @@ console.log( v );
 
 ## References
 
--   Welford, B. P. 1962. "Note on a Method for Calculating Corrected Sums of Squares and Products." _Technometrics_ 4 (3). Taylor & Francis: 419–20. doi:[10.1080/00401706.1962.10490022][@welford:1962].
+-   Welford, B. P. 1962. "Note on a Method for Calculating Corrected Sums of Squares and Products." _Technometrics_ 4 (3). Taylor & Francis: 419–20. doi:[10.1080/00401706.1962.10490022][@welford:1962a].
+-   van Reeken, A. J. 1968. "Letters to the Editor: Dealing with Neely's Algorithms." _Communications of the ACM_ 11 (3): 149–50. doi:[10.1145/362929.362961][@vanreeken:1968a].
 
 </section>
 
@@ -143,7 +144,9 @@ console.log( v );
 
 [arithmetic-mean]: https://en.wikipedia.org/wiki/Arithmetic_mean
 
-[@welford:1962]: https://doi.org/10.1080/00401706.1962.10490022
+[@welford:1962a]: https://doi.org/10.1080/00401706.1962.10490022
+
+[@vanreeken:1968a]: https://doi.org/10.1145/362929.362961
 
 </section>