fix: Don't use value for --containers flag in chart

[rossf7]

Hi @bpetit,
I found a problem with the dev branch and the --containers flag.

Removing the true value fixes it and I tested with both the dev and latest branches and it works with both.

kubectl get pods

NAME               READY   STATUS             RESTARTS     AGE
scaphandre-v7wh6   0/1     CrashLoopBackOff   1 (3s ago)   5s


kubectl logs scaphandre-v7wh6
error: unexpected value 'true' for '--containers' found; no more were expected

Usage: scaphandre prometheus --containers

For more information, try '--help'.

[bpetit]

Thanks !