docker-compose.yaml: updated default TAG to 6

Change-Id: I1c58289982033706add8a9cbb108cdf94ae12e01
Signed-off-by: Gerardo García <gerardo-garcia@users.noreply.github.com>
(cherry picked from commit ffb84c5d25b9e1123ad8d59dc406cd7132621e2f)
1 file changed