use correct api for popping back element
diff --git a/jenkins/branch/distro_builds.pipeline b/jenkins/branch/distro_builds.pipeline
index 21067df..5d8012d 100644
--- a/jenkins/branch/distro_builds.pipeline
+++ b/jenkins/branch/distro_builds.pipeline
@@ -70,7 +70,7 @@
 				script {
 					if (! env.JOB_DIR) {
 						def bparts = env.JOB_NAME.split('/')
-						bparts.pop()
+						bparts = bparts - bparts.last()
 						env.JOB_DIR = bparts.join('/')
 					}