Update k8s ingress version

Ingress is apparently no longer beta.

This is what is currently reported on the actual object in prod.

Change-Id: I94c97cb3a3afe255cd5c40c3e70a370e0adf854b
diff --git a/k8s/zuul.yaml b/k8s/zuul.yaml
index 38e1af3..3fecd9c 100644
--- a/k8s/zuul.yaml
+++ b/k8s/zuul.yaml
@@ -326,7 +326,7 @@
   domains:
     - ci.gerritcodereview.com
 ---
-apiVersion: extensions/v1beta1
+apiVersion: networking.k8s.io/v1
 kind: Ingress
 metadata:
   name: zuul-web