Fix skiptree condition.

Jenkinsfile

@@ -83,7 +83,7 @@ def findDownstreamDependencies(modules2deps, artifact) {
 def analyzeDependency(modules2deps, alreadyInTheTree, artifacts2projects, report, artifact, depth) {
     def level = "L${depth}"
     def downdeps = findDownstreamDependencies(modules2deps, artifact)
-    def skipTree = !alreadyInTheTree.contains(artifact)
+    def skipTree = alreadyInTheTree.contains(artifact)
     if (!skipTree) {
         report['downstream_modules'][level][artifact] = ['dependencies': [], 'projects': []]