Explicitely use and import dplyr::n

Fixes issues with dplyr 1.0

Change-Id: I73c59b00ee8fcc525084767d7520d6dfc4afb311
diff --git a/R/reexports.R b/R/reexports.R
index 1a4d729..1630dd9 100644
--- a/R/reexports.R
+++ b/R/reexports.R
@@ -25,6 +25,9 @@
 #' @importFrom dplyr summarise
 #' @export
 dplyr::summarise
+#' @importFrom dplyr n
+#' @export
+dplyr::n
 #' @importFrom tidyr complete
 #' @export
 tidyr::complete