Maven 3.2.3 (Aug 2014) is our current minimum required build version. For further evolution of the POMs, it might be counter-productive to go back and maintain this support (e.g.
BUILD-350, minor but still).
Besides, most devs and build tooling are operating with Maven 3.5 or 3.6 by now.
So let's bump this to 3.3.9 (Nov 2015, still a conservative baseline).