[fix] docker generated new settings.yml does not work

In commit 5a7b12ee we normalized settings.yml and c6a5cc01 and de5a8ee7 we
changed instance name to ``instance_name: "SearXNG"``.

This patch adjust the sed expressions to modify:

    dockerfiles/docker-entrypoint.sh

Closes: https://github.com/searxng/searxng/issues/876


Suggested-by:  @neiaberau
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>