tree 1c12f77fec762401c2e2dd790f4842802b68584e
parent 06746324ad28f49d86d706be3c54dc9524d166ca
author Alex Bennée <alex.bennee@linaro.org> 1571912072 +0100
committer Alex Bennée <alex.bennee@linaro.org> 1572027861 +0100

tests/docker: update Travis image to a more current version

This isn't the latest one available on hub.docker.com but it does
match the ID reported by the Xenial builds running on Travis:

  instance: ... travis-ci-sardonyx-xenial-1553530528-f909ac5

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>