Allowing delete of charts through Helm 3

Change-Id: Iac1a685a2d32cbcab547dfaf1ded473d69d4fac6
diff --git a/Jenkinsfile-voltha-build b/Jenkinsfile-voltha-build
index 844798e..c9ad668 100644
--- a/Jenkinsfile-voltha-build
+++ b/Jenkinsfile-voltha-build
@@ -47,7 +47,11 @@
                     for hchart in \$(helm list -q | grep -E -v 'docker-registry|mavenrepo|ponnet');
                     do
                         echo "Purging chart: \${hchart}"
-                        helm delete --purge "\${hchart}"
+                        if [ "$HELM_MAJOR" -le 2 ]; then
+                            helm delete --purge "\${hchart}"
+                        else
+                            helm uninstall "\${hchart}"
+                        fi
                     done
                     """
                     timeout(5) {