Update Maven PMD plugin from 3.7 to 3.8.
<disruptorVersion>3.3.7</disruptorVersion>
<conversantDisruptorVersion>1.2.10</conversantDisruptorVersion> <!-- Version 1.2.11 requires Java 8 -->
<compiler.plugin.version>3.7.0</compiler.plugin.version>
- <pmd.plugin.version>3.7</pmd.plugin.version>
+ <pmd.plugin.version>3.8</pmd.plugin.version>
<findbugs.plugin.version>3.0.5</findbugs.plugin.version>
<changes.plugin.version>2.12.1</changes.plugin.version>
<javadoc.plugin.version>3.0.0-M1</javadoc.plugin.version>
