Fixes https://issues.jenkins-ci.org/browse/JENKINS-12764

Taken from commit (https://github.com/vcarluer/violations-plugin/commit/b25c6e545834297938a76f039ac81244fb43a87d).  This fixes the problem with the Violations Summary.  All the other changes in PR https://github.com/jenkinsci/violations-plugin/pull/12 is extra.

This one change fixes the issue for Jenkins 1.457 at least.  Older versions of Violations plugin do not work on Jenkins  even though it works on Hudson builds.   Please review!  Thanks.