Rev 0.8.3 (djenriquez#18)

Allow to override default environment variables values (djenriquez#14)

Defaults are the same as before, but they can now be overridden if
needed.
The README has been reflected to explain the use case.

revved the NOMAD_VERSION (djenriquez#10)

Fix gpg keyserver endpoint

Upgrading to 0.7.0 Beta

Upgrade alpine base image + add release 0.6.3

Add release 0.6.0

Bump Nomad version to 0.5.6

Merge pull request djenriquez#3 from briansorahan/master

add tzdata

Adding release 0.5.5