(doc) Fix iterated collection

Author: pzygielo

src/main/java/org/apache/maven/plugins/shade/mojo/ShadeMojo.java

@@ -785,7 +785,7 @@ private void processArtifactSelectors( Set<File> artifacts, Set<String> artifact
         {
             getLog().warn( "Skipping empty test jar " + artifactId + "." );
         }
-        for ( String artifactId : emptyTestArtifacts )
+        for ( String artifactId : emptyTestSourceArtifacts )
         {
             getLog().warn( "Skipping empty test source jar " + artifactId + "." );
         }