fix some markup errors
diff --git a/Doc/lib/liblogging.tex b/Doc/lib/liblogging.tex
index 4bb0595..f9c1d72 100644
--- a/Doc/lib/liblogging.tex
+++ b/Doc/lib/liblogging.tex
@@ -1531,7 +1531,7 @@
\var{exc_info} is the exception tuple obtained by calling
\function{sys.exc_info() }(or \constant{None}, if no exception information
is available). The \var{func} is the name of the function from which the
-logging call was made. If not specified, it defaults to \var{None}.
+logging call was made. If not specified, it defaults to \code{None}.
\versionchanged[\var{func} was added]{2.5}
\end{classdesc}