ECS agent is outdated

[martinkoch-geniebelt]

The ECS agent in the pre-built ami (at least the one in eu-west-1, ami-c41f3bb7) is 1.13.1, but the current version is 1.14.3. I'm not familiar enough with packer to roll my own new image, so I was wondering if you could please build a set of new amis (and update https://github.com/segmentio/stack/blob/master/defaults/main.tf#L25 accordingly).

[Brzhk]

#139 fixes the problem, and the latest agent will be picked up by the host instances when restarted.
Unfortunately, docker-engine/docker-engine will not, and the instances will still require to be restarted manually.