Upgraded Checkstyle version to 8.21
Upgraded Checkstyle version to 8.21

apache/mina-sshd,apache/mina-sshd,lgoldstein/mina-sshd,lgoldstein/mina-sshd,apache/mina-sshd,apache/mina-sshd,lgoldstein/mina-sshd,lgoldstein/mina-sshd