Upgrade sortpom-maven-plugin 3.0.1 -> 3.1.3 (#213)

See:
- https://github.com/Ekryd/sortpom/wiki/Versions
- https://github.com/Ekryd/sortpom/releases/tag/sortpom-parent-3.1.0
- https://github.com/Ekryd/sortpom/releases/tag/sortpom-parent-3.1.1
- https://github.com/Ekryd/sortpom/releases/tag/sortpom-parent-3.1.2
- https://github.com/Ekryd/sortpom/releases/tag/sortpom-parent-3.1.3
- Ekryd/sortpom@sortpom-parent-3.0.1...sortpom-parent-3.1.3

pom.xml

@@ -229,7 +229,7 @@
                 <plugin>
                     <groupId>com.github.ekryd.sortpom</groupId>
                     <artifactId>sortpom-maven-plugin</artifactId>
-                    <version>3.0.1</version>
+                    <version>3.1.3</version>
                     <configuration>
                         <createBackupFile>false</createBackupFile>
                         <encoding>${project.build.sourceEncoding}</encoding>