Update link to pbzip2 website.

Website for pbzip2 does not exist anymore, now seems to be hosted at: http://compression.great-site.net/pbzip2/ Downloading [pbzip2_1.1.13.orig.tar.gz](https://launchpad.net/ubuntu/+archive/primary/+sourcefiles/pbzip2/1.1.13-1build1/pbzip2_1.1.13.orig.tar.gz) from https://launchpad.net/ubuntu/+source/pbzip2/1.1.13-1build1 and looking in `AUTHORS` lists the following website: https://gilchrist.great-site.net/jeff/, which lists: http://compression.great-site.net/pbzip2/ , so I guess it is save to assume that this is owned by the original developer.