fix cstyle link

Author: Vladimir Kotal

intro.tex

@@ -604,7 +604,7 @@
 \item A process that runs C style check script before integration into a source
 code repository automatically and refuses to accept any changesets not following
 the chosen C style is a working solution to avoid C style violations.
-\item \url{http://mff.devnull.cz/cstyle.html}
+\item \url{http://mff.devnull.cz/cstyle/}
 \end{itemize}
 
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