config: bump checkstyle plugin version to 3.1.2
config: bump checkstyle plugin version to 3.1.2

checkstyle/contribution,rnveach/contribution,checkstyle/contribution,checkstyle/contribution,rnveach/contribution,rnveach/contribution,rnveach/contribution,checkstyle/contribution,checkstyle/contribution,checkstyle/contribution,rnveach/contribution,rnveach/contribution,rnveach/contribution,checkstyle/contribution