Fix the version number in which changes were made

Doc/lib/libtime.tex

@@ -164,7 +164,7 @@ used.  \code{ctime(\var{secs})} is equivalent to
 Locale information is not used by \function{ctime()}.
 \versionchanged[Allowed \var{secs} to be omitted]{2.1}
 \versionchanged[If \var{secs} is \constant{None}, the current time is
-                used]{2.3}
+                used]{2.4}
 \end{funcdesc}
 
 \begin{datadesc}{daylight}
@@ -179,7 +179,7 @@ provided or \constant{None}, the current time as returned by
 above for a description of the \class{struct_time} object.
 \versionchanged[Allowed \var{secs} to be omitted]{2.1}
 \versionchanged[If \var{secs} is \constant{None}, the current time is
-                used]{2.3}
+                used]{2.4}
 \end{funcdesc}
 
 \begin{funcdesc}{localtime}{\optional{secs}}
@@ -189,7 +189,7 @@ not provided or \constant{None}, the current time as returned by
 applies to the given time.
 \versionchanged[Allowed \var{secs} to be omitted]{2.1}
 \versionchanged[If \var{secs} is \constant{None}, the current time is
-                used]{2.3}
+                used]{2.4}
 \end{funcdesc}
 
 \begin{funcdesc}{mktime}{t}