games/factorio: default proxyImage to version in proxy.libsonnet

Change-Id: Ic4c793311bc6ac6e3194a7b1464bb21d4ad7d1bd
diff --git a/games/factorio/kube/factorio.libsonnet b/games/factorio/kube/factorio.libsonnet
index 538500c..6684fc0 100644
--- a/games/factorio/kube/factorio.libsonnet
+++ b/games/factorio/kube/factorio.libsonnet
@@ -1,6 +1,7 @@
 # Factorio on Kubernetes.
 
 local kube = import "../../../kube/kube.libsonnet";
+local proxy = import "proxy.libsonnet";
 
 {
     local factorio = self,
@@ -11,7 +12,7 @@
         appName: "factorio",
         storageClassName: "waw-hdd-redundant-3",
         prefix: "", # if set, should be 'foo-'
-        proxyImage: error "proxyImage must be set",
+        proxyImage: proxy.cfg.image,
 
         rconPort: 2137,
         rconPassword: "farts",