H5: Fix translation

exercises/h5.md

@@ -911,7 +911,7 @@ More about Port Knocking technique:
 
 - [Improved Port Knocking with Strong Authentication - Rennie deGraaf, John Aycock, and Michael Jacobson, Jr.∗ (Department of Computer Science - University of Calgary)](https://www.acsac.org/2005/papers/156.pdf)
 
-- [OpenWRT:n sivut](https://wiki.openwrt.org/doc/howto/portknock.server)
+- [OpenWRT website](https://wiki.openwrt.org/doc/howto/portknock.server)
 
 - [portknocking.org](http://www.portknocking.org/) and practical solutions on [Implementations sub-page](http://www.portknocking.org/view/implementations)