This appears to be a small update compared to other recent updates. In
particular the dockerfile has not changed and neither have the
settings.json files. The changelog can be found here:
https://github.com/ether/etherpad-lite/blob/v2.2.6/CHANGELOG.md
The only notable update there is that pads can be deleted by their
creators. I suspect this is a noop for us since we don't do
authenticated access, but we should check with a held node.
Change-Id: I4e935828912d004eb7694e981926557db8b26e56
deb04db7f4