upgrade parent and activate Reproducible Builds

Author: hboutemy

pom.xml

@@ -4,7 +4,7 @@
   <parent>
     <groupId>org.codehaus.plexus</groupId>
     <artifactId>plexus</artifactId>
-    <version>5.1</version>
+    <version>6.1</version>
   </parent>
 
   <artifactId>plexus-interpolation</artifactId>
@@ -31,7 +31,10 @@
     </site>
   </distributionManagement>
 
-
+  <properties>
+    <project.build.outputTimestamp>2020-01-20T18:52:37Z</project.build.outputTimestamp>
+  </properties>
+  
   <build>
     <plugins>
       <plugin>