Dropbox will soon require ext4 - container currently using ext2

I've been getting emails recently, which I've just realised are valid, that Dropbox will soon no longer support anything but ext4 ([best source from those emails](https://www.dropbox.com/help/desktop-web/system-requirements))

The container at least is currently showing:
`root@host:/dbox/Dropbox# fsck -N /dev/sdb1
fsck from util-linux 2.25.2
[/sbin/fsck.ext2 (1) -- /dev/sdb1] fsck.ext2 /dev/sdb1
root@host:/dbox/Dropbox#`

I'll research as soon as I can how to make the change as I think this is likely more Docker related, but just in case I don't...

The issue names no repository files, tests, or entry points. Start by reviewing the container's filesystem setup and the linked Dropbox system requirements, then use the discussion to determine whether the image or runtime controls the filesystem type. Done should be a documented, reproducible resolution for Dropbox's ext4 requirement.

Written by the indexing model from the issue text.