docker installs need a `chown` for `files/`
a bunch of people have reported recently that a newly-started docker sharkey can't write to files/
until it's chown
-ed to 991
that should either not be necessary, or be documented better (we only have that bit in the "upgrade" notes)
this could be caused by any of:
- not running as root (we're not going back to running as root!)
- changing the way the directory is created by sharkey (unlikley, but we did change it)
- changing the way the directory is created inside the container
- something else?