build: update cloudbuild config for building tools to use k8s 1.11

Author: droot

build/cloudbuild_tools.yaml

@@ -13,7 +13,7 @@
 #  limitations under the License.
 
 steps:
-- name: "gcr.io/kubebuilder/thirdparty-${_GOOS}:1.10.1"
+- name: "gcr.io/kubebuilder/thirdparty-${_GOOS}:1.11.0"
   args: ["cp", "/kubebuilder_${_GOOS}_${_GOARCH}.tar.gz", "/workspace/kubebuilder-${TAG_NAME}-${_GOOS}-${_GOARCH}.tar.gz"]
   env:
   - 'GOOS=${_GOOS}'