Update maintainer list

[skip ci]

libs/maintainers.txt

@@ -65,6 +65,7 @@ graph                 K. Noel Belcourt <kbelco -at- sandia.gov>
 graph_parallel        K. Noel Belcourt <kbelco -at- sandia.gov>
 hana                  Louis Dionne <ldionne.2 -at- gmail.com>
 heap                  Tim Blechmann <tim -at- klingt.org>
+histogram             Hans Dembinski <hans.dembinski@gmail.com>
 hof                   Paul Fultz II <pfultz2 -at- yahoo.com>
 icl                   Joachim Faulhaber <afojgo -at- gmail.com>
 integer               Daryle Walker <darylew -at- hotmail.com>, Andrey Semashev <andrey.semashev -at- gmail.com>