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/var-substitution/kustomization.yaml

@@ -0,0 +1,11 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+  - ./deployment.yaml
+generatorOptions:
+  labels:
+    kustomize.toolkit.fluxcd.io/substitute: disabled
+configMapGenerator:
+  - name: flux-grafana-dashboards
+    files:
+      - cluster.json