Set version for maven-antrun-plugin

It was missing but should be defined for reproducibility.

Version 1.3 was used so far. This version is configured in
maven-model-builder which implicitly is used as super pom.

pom.xml

@@ -336,6 +336,10 @@
     <finalName>${project.artifactId}</finalName>
     <pluginManagement>
       <plugins>
+        <plugin>
+          <artifactId>maven-antrun-plugin</artifactId>
+          <version>1.8</version>
+        </plugin>
         <plugin>
           <artifactId>maven-clean-plugin</artifactId>
           <version>3.1.0</version>