Fix markup error.

Doc/lib/libtraceback.tex

@@ -119,7 +119,7 @@ A shorthand for \code{format_list(extract_stack(\var{f}, \var{limit}))}.
 \begin{funcdesc}{tb_lineno}{tb}
 This function returns the current line number set in the traceback
 object.  This function was necessary because in versions of Python
-prior to 2.3 when the \programopt{O} flag was passed to Python the
+prior to 2.3 when the \programopt{-O} flag was passed to Python the
 \code{\var{tb}.tb_lineno} was not updated correctly.  This function
 has no use in versions past 2.3.
 \end{funcdesc}