Bug#988099: It works, the default is just wront

[Jürgen Richtsfeld]

I just found that if I put "--collector.diskstats" in the ARGS of
/etc/default/prometheus-node-exporter and restart the service it works.
I didn't try this i in the first row as the documentation says that this
is default enabled anyways (so the bug basically just is, that the
description about the default is wrong!).