[server] fix generate_source_config regression on python2
lgc outputs "str" objects on python2 and python3, so we can't just use
io.StringIO (which expects unicode objects).
Fixes: c36cda9074c5
#! /bin/sh -e
case "$1" in
configure|abort-upgrade|abort-remove|abort-deconfigure)
update-rc.d cubicweb defaults 99 >/dev/null
;;
*)
echo "postinst called with unknown argument \`$1'" >&2
exit 1
;;
esac
#DEBHELPER#
exit 0