Corrected a typo in args-group.R

Author: fweber144

man-roxygen/args-group.R

@@ -1,3 +1,3 @@
-#' @param group A grouping variable (a vector or factor) the same length as
+#' @param group A grouping variable (a vector or factor) of the same length as
 #'   `y`. Each value in `group` is interpreted as the group level
 #'   pertaining to the corresponding value of `y`.