Fix missing parenthesis.

Doc/lib/libdatetime.tex

@@ -902,7 +902,7 @@ Instance methods:
 
 \begin{methoddesc}{isoweekday}{}
   Return the day of the week as an integer, where Monday is 1 and
-  Sunday is 7.  The same as \code{self.date().isoweekday)}.
+  Sunday is 7.  The same as \code{self.date().isoweekday()}.
   See also \method{weekday()}, \method{isocalendar()}.
 \end{methoddesc}