Make scripts/cjdns.sh default to flat conffile layout

scripts/cjdns.sh currently assumes that the config file is located one directory above the cjdroute binary. This seems to be not the case, because the official installation instructions tell you to run it with "./cjdroute", and that's what people usually do. This results in the config file skeleton being written to the directory in which cjdroute binary resides.

This pull request makes scripts/cjdns.sh default to the location of the config file described in the scenario above. Among other things it's required to keep the Debian instructions at hyperboria.net simple.