[R-package] [docs] add Michael Mayer to DESCRIPTION (#4867)

R-package/DESCRIPTION

@@ -26,7 +26,8 @@ Authors@R: c(
     person("Daniel", "Lemire", role = c("ctb")),
     person("Victor", "Zverovich", role = c("cph")),
     person("IBM Corporation", role = c("ctb")),
-    person("David", "Cortes", role = c("ctb"))
+    person("David", "Cortes", role = c("ctb")),
+    person("Michael", "Mayer", role = c("ctb"))
     )
 Description: Tree based algorithms can be improved by introducing boosting frameworks.
     'LightGBM' is one such framework, based on Ke, Guolin et al. (2017) <https://papers.nips.cc/paper/6907-lightgbm-a-highly-efficient-gradient-boosting-decision>.