completing ref

Author: lemire

README.md

@@ -167,7 +167,7 @@ If you have ``doxygen`` installed, you can type ``make doxygen`` and create a do
 Please see
 
 
-* Daniel Lemire, Owen Kaser, Nathan Kurz, Luca Deri, Chris O'Hara, François Saint-Jacques, Gregory Ssi-Yan-Kai, Roaring Bitmaps: Implementation of an Optimized Software Library, Software: Practice and Experience (to appear) [arXiv:1709.07821](https://arxiv.org/abs/1709.07821)
+* Daniel Lemire, Owen Kaser, Nathan Kurz, Luca Deri, Chris O'Hara, François Saint-Jacques, Gregory Ssi-Yan-Kai, Roaring Bitmaps: Implementation of an Optimized Software Library, Software: Practice and Experience 48 (4), 2018 [arXiv:1709.07821](https://arxiv.org/abs/1709.07821)
 * Daniel Lemire, Owen Kaser, Kamel Aouiche, Sorting improves word-aligned bitmap indexes. Data & Knowledge Engineering 69 (1), pages 3-28, 2010. http://arxiv.org/abs/0901.3751
 * Owen Kaser and Daniel Lemire, Compressed bitmap indexes: beyond unions and intersections, Software: Practice and Experience 46 (2), 2016. http://arxiv.org/abs/1402.4466