[R-package] update roles in DESCRIPTION (#5192)

R-package/DESCRIPTION

@@ -26,7 +26,7 @@ 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("aut")),
     person("Michael", "Mayer", role = c("ctb"))
     )
 Description: Tree based algorithms can be improved by introducing boosting frameworks.