Upgrade node to 18

Matches version in os package manager.

Change-Id: I3fe0383119d843a1e40c492b02cf544a0f5ce112
diff --git a/playbooks/gerrit-setup/pre.yaml b/playbooks/gerrit-setup/pre.yaml
index a36d397..c608012 100644
--- a/playbooks/gerrit-setup/pre.yaml
+++ b/playbooks/gerrit-setup/pre.yaml
@@ -5,6 +5,6 @@
     - role: ensure-java
       java_version: 17
     - role: ensure-nodejs
-      node_version: 12
+      node_version: 18
     - install-build-essential
     - prepare-gerrit-repos