Fix shell invocation in gui-unit.yaml

Change-Id: Ieb8dfb46aa32ab62eeda50116bd5c003ea7a099f
diff --git a/jjb/gui-unit.yaml b/jjb/gui-unit.yaml
index 1cfd3c0..a4c315c 100644
--- a/jjb/gui-unit.yaml
+++ b/jjb/gui-unit.yaml
@@ -39,8 +39,11 @@
     project-type: freestyle
     concurrent: true
 
-    shell: |
-      npm install
-      npm run lint
-      npm test
+    builders:
+      - shell: |
+          #/usr/bin/env bash
+          set -eu -o pipefail
+          npm install
+          npm run lint
+          npm test