Checkstyle 6.8 release brake compatibility with gradle checkstyle plugin

Checkstyle issue: https://github.com/checkstyle/checkstyle/issues/1108 description of required code update was added.

Error : https://travis-ci.org/sevntu-checkstyle/checkstyle-samples/jobs/68755365

Please update checkstyle plugin to be compatible with Checkstyle 6.8

This has been reported in another topic.