NIFIREG-364 - Upgraded again to checkstyle 8.31.
NIFIREG-364 - Upgraded again to checkstyle 8.31.

Signed-off-by: Arpad Boda <aboda@apache.org>

This closes #270

scottyaslan/nifi-registry,scottyaslan/nifi-registry,scottyaslan/nifi-registry,scottyaslan/nifi-registry