Fix a type error.

Change-Id: I99c9aab8b1e7c0da4c77083814853d037fb7b8e4
diff --git a/cicd/pipelines/enterprise/image_unstable.jenkins b/cicd/pipelines/enterprise/image_unstable.jenkins
index 4635577..3079258 100644
--- a/cicd/pipelines/enterprise/image_unstable.jenkins
+++ b/cicd/pipelines/enterprise/image_unstable.jenkins
@@ -17,8 +17,8 @@
                                         privileged: true)
 def aptlyVolume = persistentVolumeClaim(claimName: 'aptly-state', mountPath: '/var/lib/aptly')
 def envVars = [
-    'IS_JENKINS=true',
-    'RELEASE_NAME=unstable'
+    'IS_JENKINS': 'true',
+    'RELEASE_NAME': 'unstable'
 ]
 
 podTemplate(label: buildLabel, containers: [jnlpContainer, debianContainer], volumes: [aptlyVolume], envVars: envVars) {