I have zero idea if we have IE6 clients any more, but according to the
H5BP community IE6 actually did support gzip and only represents 0.1%
of Internet traffic in 2015 (!) anyways.
See: https://github.com/h5bp/server-configs-nginx/issues/125
Using www-data was a temporary measure while I was waiting for the
official nginx.org packages to be released for Debian 9 and we had
to use Debian's own nginx package.
There are currently no nginx.org builds for Debian 9, so we need to
use the package from Debian's repository. This package provides a
www-data user and group instead of an nginx one.
We can revert some of this after Debian 9 is released and official
builds come from nginx.org (though it might be useful to keep the
main nginx.conf as a template).
