Update reference in README.md (#202)

* Update reference in README.md

* Update README.md

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Co-authored-by: David Widmann <[email protected]>

Author: matbesancon

README.md

@@ -61,5 +61,5 @@ Contributors include:
 - Peyré, G. and Cuturi, M., 2019. Computational optimal transport. Foundations and Trends® in Machine Learning, 11(5-6), pp.355-607.
 - Lorenz, D.A., Manns, P. and Meyer, C., 2019. Quadratically regularized optimal transport. Applied Mathematics & Optimization, pp.1-31.
 - Rémi Flamary and Nicolas Courty, POT Python Optimal Transport library, https://pythonot.github.io/, 2017
-- Chizat, L., Peyré, G., Schmitzer, B. and Vialard, F.X., 2016. Scaling algorithms for unbalanced transport problems. arXiv preprint arXiv:1607.05816.
+- Chizat, L., Peyré, G., Schmitzer, B. and Vialard, F.X., 2018. Scaling algorithms for unbalanced transport problems. Mathematics of Computation, 87(314), pp.2563-2609.
 - Schmitzer, B., 2019. Stabilized sparse scaling algorithms for entropy regularized transport problems. SIAM Journal on Scientific Computing, 41(3), pp.A1443-A1481.