Set node version for javascript publish job

The build jobs set node version to 8, make sure the publish job is too.

Change-Id: I051f3a1b4bc6f0b458d9be66badff6bb04b4beaf
diff --git a/.zuul.yaml b/.zuul.yaml
index 0ddfa25..300107c 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -114,4 +114,6 @@
       jobs:
         - publish-openstack-sphinx-docs-infra-python3
         - publish-openstack-python-branch-tarball
-        - publish-openstack-javascript-content
+        - publish-openstack-javascript-content:
+            vars:
+                node_version: 8