DO NOT MERGE: jitpack based zipkin build

[codefromthecrypt]

So, we should figure out how to cut images mostly for master, but possibly for feature branches also. This is just a dockerfile edit, but maybe helpful to start elaborating what something real might look like.

cc @openzipkin/devops-tooling

[codefromthecrypt]

@yyyogev you may also be interested in this. We've been toying with different ways to deliver pending changes to users easier so that our final builds are more stable and relevant.

[codefromthecrypt]

ps those building will need to use something like this as nothing in the dockerfile changes from builld-to-build docker build --no-cache -t adriancole/zipkin zipkin