Update maven-pmd-plugin from 3.6 to 3.7.
diff --git a/pom.xml b/pom.xml
index db100e9..cfe9395 100644
--- a/pom.xml
+++ b/pom.xml
@@ -46,7 +46,7 @@
     <commons.release.version>${project.version}</commons.release.version>
     <commons.rc.version>RC1</commons.rc.version>
     <powermock.version>1.6.4</powermock.version>
-    <commons.pmd-plugin.version>3.6</commons.pmd-plugin.version>
+    <commons.pmd-plugin.version>3.7</commons.pmd-plugin.version>
   </properties>
 
   <issueManagement>