Fix Knoppix 3.1 link

[ViMan 0]

The link on the web site for Knoppix 3.1 does not work (http://www.knopper.net/knoppix/index-en.htm) because you forgot an l at the at the end of the URL. It should be http://www.knopper.net/knoppix/index-en.html

[Philipp 6]

Thanks