Document dependency on recent docker version

[banks]

Hi,

Honestly I don't know if this is at all actionable but just wanted to provide some feedback on an issue I had. Perhaps could add a note to README?

I used the old fig version of this fine and then recently pulled master to use docker-compose now it has changed name.

I'm on OS X with boot2docker but I had docker 1.2.0 still.

Building the kafka image here failed due to inability to fetch from apache mirrors with cryptic return value (8). But I noticed that the env vars were wonky inside the docker container. This is result of logging directly into the intermediate container that was used in the failed build step:

$ docker run -ti a5ee51dafb97 /bin/bash
root@5bbb832addc7:/# echo ${KAFKA_VERSION}
"0.8.2.0"=SCALA_VERSION="2.10"
root@5bbb832addc7:/# echo ${SCALA_VERSION}

root@5bbb832addc7:/# exit
exit

I'm not sure if support for multiple ENV assignments on one line was a recent addition (docs don't say when it was introduced) or if something else was going on but upgrading to docker 1.5.0 seems to have fixed whatever the issue was...

If you care about supporting older docker, you could go back to ENV FOO BAR syntax which apparently works but I'm not really sure it's worth your time - you might like to add a note to README though.

[sscaling]

Hmm, definitely sounds like a bug in docker. We essentially test against the latest stable docker release which can now be seen in the travis logs, e.g. https://travis-ci.org/wurstmeister/kafka-docker/builds/359722608?utm_source=github_status&utm_medium=notification

Probably still worth adding a note to the README.