Add missing right-parenthesis.

Doc/lib/libpty.tex

@@ -23,7 +23,7 @@ Return value is \code{(\var{pid}, \var{fd})}. Note that the child
 gets \var{pid} 0, and the \var{fd} is \emph{invalid}. The parent's
 return value is the \var{pid} of the child, and \var{fd} is a file
 descriptor connected to the child's controlling terminal (and also
-to the child's standard input and output.
+to the child's standard input and output).
 \end{funcdesc}
 
 \begin{funcdesc}{openpty}{}