Set DNS listening mode to 'ALL' in docker-compose.yml example

[cornshakes]

What does this PR aim to accomplish?:

It changes the docker-compose example listening mode to 'ALL', because 'all' doesn't work (anymore?).

How does this PR accomplish the above?:

The current docker-compose file example contains this environment variable:

FTLCONF_dns_listeningMode: 'all'

This was changed to

FTLCONF_dns_listeningMode: 'ALL'

to reflect the current documentation.

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