Update pkg/kustomize to v0.1.0

If implemented this fixes a bug where retrieving the groupVersion.Group
of a kustomization were returning an empty string.

Signed-off-by: Soule BA <soule@weave.works>

cmd/flux/testdata/build-kustomization/podinfo-kustomization.yaml

@@ -13,3 +13,7 @@ spec:
     kind: GitRepository
     name: podinfo
   targetNamespace: default
+  postBuild:
+    substitute:
+      cluster_env: "prod"
+      cluster_region: "eu-central-1"