Add absolute path to validate_manifest.sh

Change-Id: Ib6715829883b1a09560b253a3c80ecedda41f225
diff --git a/Jenkinsfile b/Jenkinsfile
index 117f70c..3fa899a 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -28,7 +28,7 @@
 }
 
 def validateXMLwithDTD() {
-    sh returnStdout: true, script: './validate_manifest.sh'
+    sh returnStdout: true, script: env.WORKSPACE + '/validate_manifest.sh'
 }
 
 int checkBranchExists(def proj) {