Shouldn't use m.g.o-public as repository anymore.
Setting up repo.jenkins-ci.org as a mirror for it as described in
https://wiki.jenkins-ci.org/display/JENKINS/Plugin+tutorial
works around the problem, but IMO would be better if that wouldn't be
needed in the 1st place
[Fixed JENKINS-9693] maven.build.timestamp.format is not obeyed in maven
builds (integrate maven-interceptors 1.5)
[FIXED JENKINS-21279]

Not sure packaging doesn't defeault to "jar", which seems to be the default, but being defensive.