Updating checkstyle plugin

git-svn-id: https://svn.apache.org/repos/asf/syncope/branches/1_1_X@1593497 13f79535-47bb-0310-9956-ffa450edef68
SYNCOPE-485 Upgrade to Activity 5.15.1

git-svn-id: https://svn.apache.org/repos/asf/syncope/branches/1_1_X@1593516 13f79535-47bb-0310-9956-ffa450edef68
Merge from 1_1_X

git-svn-id: https://svn.apache.org/repos/asf/syncope/trunk@1593543 13f79535-47bb-0310-9956-ffa450edef68