Fix dead link (#21)

lkmpg.tex

@@ -868,7 +868,7 @@ If you want more information, you can read this web page:
 \begin{itemize}
 \item \url{http://lwn.net/Articles/22355/}
 
-\item \url{http://www.kernelnewbies.org/documents/seq\_file\_howto.txt}
+\item \url{https://kernelnewbies.org/Documents/SeqFileHowTo}
 \end{itemize}