Fix maven warning about plugin version (#568)

pf4j/pom.xml

@@ -23,6 +23,7 @@
             <plugin>
                 <groupId>org.codehaus.mojo</groupId>
                 <artifactId>templating-maven-plugin</artifactId>
+                <version>3.0.0</version>
                 <executions>
                     <execution>
                         <id>filter-src</id>