Fix wrong logstash-forwarder.conf scan paths

Tried to fix https://github.com/digital-wonderland/docker-logstash-forwarder/issues/1.
Works for me, but I had to replace all occurrences of `digital-wonderland/docker-logstash-forwarder` with `dryewo/docker-logstash-forwarder`. You don't have to merge it.
The only real change is in `forwarder/config/config.go`.