build(pom.xml): update maven-pmd-plugin to 3.12.0

This also updates PMD to 6.13.0

Changelogs:
- https://www.mail-archive.com/[email protected]/msg00824.html
- https://www.mail-archive.com/[email protected]/msg00853.html
- https://www.mail-archive.com/[email protected]/msg00878.html
- https://www.mail-archive.com/[email protected]/msg00905.html
- https://pmd.github.io/2017/05/20/PMD-5.7.0/
- https://pmd.github.io/2017/06/24/PMD-5.8.0/
- https://pmd.github.io/2017/07/01/PMD-5.8.1/
- https://pmd.github.io/2017/12/15/PMD-6.0.0/
- https://pmd.github.io/2018/01/21/PMD-6.0.1/
- https://pmd.github.io/2018/02/25/PMD-6.1.0/
- https://pmd.github.io/2018/03/26/PMD-6.2.0/
- https://pmd.github.io/2018/04/29/PMD-6.3.0/
- https://pmd.github.io/2018/05/29/PMD-6.4.0/
- https://pmd.github.io/2018/06/26/PMD-6.5.0/
- https://pmd.github.io/2018/07/29/PMD-6.6.0/
- https://pmd.github.io/2018/09/02/PMD-6.7.0/
- https://pmd.github.io/2018/09/30/PMD-6.8.0/
- https://pmd.github.io/2018/10/28/PMD-6.9.0/
- https://pmd.github.io/2018/12/09/PMD-6.10.0/
- https://pmd.github.io/2019/01/27/PMD-6.11.0/
- https://pmd.github.io/2019/02/24/PMD-6.12.0/
- https://pmd.github.io/2019/03/31/PMD-6.13.0/

No functional changes.

Fix #1014

Author: php-coder

pom.xml

@@ -552,7 +552,7 @@
 
 		<native2ascii.plugin.version>2.0.1</native2ascii.plugin.version>
 		<owasp-plugin.version>3.0.2</owasp-plugin.version>
-		<pmd.plugin.version>3.8</pmd.plugin.version>
+		<pmd.plugin.version>3.12.0</pmd.plugin.version>
 		<resources.plugin.version>3.1.0</resources.plugin.version>
 		<robotframework-plugin.version>1.4.7</robotframework-plugin.version>
 		<robotframework-selenium.version>2.53.1.1</robotframework-selenium.version>