[MPOM-114] added missing org.apache.maven.plugins groupId for consistency

git-svn-id: https://svn.apache.org/repos/asf/maven/pom/trunk@1743283 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/asf/pom.xml b/asf/pom.xml
index c61e10f..d48d8cc 100644
--- a/asf/pom.xml
+++ b/asf/pom.xml
@@ -325,6 +325,7 @@
                project directory source structure. This is the artifact which is
                the official subject of any release vote. -->
           <plugin>
+            <groupId>org.apache.maven.plugins</groupId>
             <artifactId>maven-assembly-plugin</artifactId>
             <dependencies>
               <dependency>