Fix no-visible-binding-for-global-variable-note-in-r-cmd-check

Change-Id: Icb4ecdb2a3d02bbae8bef7c21d03b88a7107a4d2
diff --git a/NAMESPACE b/NAMESPACE
index 534fbd3..e7aa324 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -86,6 +86,7 @@
 importFrom(dplyr,summarise)
 importFrom(dplyr,tibble)
 importFrom(dplyr,ungroup)
+importFrom(dplyr,where)
 importFrom(ggplot2,GeomPoint)
 importFrom(ggplot2,aes)
 importFrom(ggplot2,element_text)