typo fix

man/duplicated.Rd

@@ -44,7 +44,7 @@ the reverse side, i.e., the last (or rightmost) of identical elements would
 correspond to \code{duplicated = FALSE}.}
 \item{by}{\code{character} or \code{integer} vector indicating which combinations 
 of columns from \code{x} to use for uniqueness checks. By default all columns are
-are being used. The was changed recently for consistency to data.frame methods.
+are being used. That was changed recently for consistency to data.frame methods.
 In version \code{< 1.9.8} default was \code{key(x)}.}
 \item{na.rm}{Logical (default is \code{FALSE}). Should missing values (including 
 \code{NaN}) be removed?}