pom.xml(maven-checkstyle-plugin): updated to 2.11

@see http://mail-archives.apache.org/mod_mbox/maven-announce/201311.mbox/%3CCALhtWkesjOD6WbN9HET7JMc7VJNjwYPNWCGbTevhb%2By_0ZK5NQ%40mail.gmail.com%3E

No functional changes.

[ci skip]
pom.xml: remove empty <configuration> section.

Should be in 57cec5f8a48e8f46581fb6088018d8b468124dc1 commit.

No functional changes.

[ci skip]
SuspiciousActivity: rename a field (and column) to fix a typo in name.

Spotted by IntelliJ IDEA.

No functional changes.