Remove usage of GStrings.

Jenkinsfile

@@ -78,7 +78,7 @@ def findDownstreamDependencies(modules2deps, artifact) {
 
 //build the report of the given dependency, go recursive on its dependencies
 def analyzeDependency(modules2deps, artifacts2projects, report, artifact, depth) {
-    GString level = "L${depth}"
+    def level = "L${depth}"
     report['downstream_modules'][level][artifact] = ['dependencies': [], 'projects': []]
 
     // get all downstream dependencies
@@ -105,8 +105,8 @@ def analyzeDependency(modules2deps, artifacts2projects, report, artifact, depth)
 
 // print the final report
 def printReport(report) {
-    GString text = ''
-    String indent = '\t'
+    def text = ''
+    def indent = '\t'
     text += "Dependency Report for ${report['project']} (jenkins project)"
     text += "\n\n"
     text += "|--Project Maven Modules\n"