Upgrade PMD plugin to 3.2 to check for use of multiple SLF4j Loggers in a single class

About a month ago, I submitted a fix to the PMD project as part of [Resolved PMD Violation: MoreThanOneLogger](https://github.com/Adobe-Consulting-Services/acs-aem-commons/pull/237). That fix has come of age, and is now part of maven-pmd-plugin:3.2.

I took the initiative to upgrade the maven-pmd-plugin in the parent pom to the latest version in order to bring the latest PMD-approved slf4j-flavored monologging to the entire ACS AEM Commons project. 

As an added bonus, I have already resolved the four new PMD violations introduced by the upgrade, which means this pull request is worth at least five times as much as it would have been if I hadn't submitted it at all.