Starting with namespace parameter doesn't work

When trying to run the docker image with the namespace  parameter like this:
```
docker run --rm -p 5678:5678 ennexa/resque-web -N my_namespace  -r redis://10.21.220.138:6379
```
The resque-web is started, but the namespace is not propagated (I can't see the workers nor the jobs). When I try directly installing the resque-web gem and running it with the -N parameter, everything works well