The InferenceService "sklearn-iris" is invalid: metadata.managedFields.fieldsType: Invalid value: "": must be `FieldsV1`

/kind bug

What steps did you take and what happened: I am trying to test KFServing Installation, setting up for the first time from Test KFServing Installation . Not really sure if its a bug?

Commands shown below

kubectl create namespace kfserving-test
kubectl apply -f docs/samples/sklearn/sklearn.yaml -n kfserving-test

Error message:

The InferenceService "sklearn-iris" is invalid: metadata.managedFields.fieldsType: Invalid value: "": must be `FieldsV1`

What did you expect to happen:

$ inferenceservice.serving.kubeflow.org/sklearn-iris created

Anything else you would like to add:

• I have got istio installed with manifest from Installing Istio without sidecar injection and Knative components using Operators
• Not sure if its an issue with any of the versions i am using?

$ kubectl get pods --namespace knative-serving
NAME                                READY   STATUS     RESTARTS   AGE
activator-6d9f95b7f8-k5gtd          2/2     Running    0          24m
autoscaler-597fd8d69d-b6htb         2/2     Running    0          24m
autoscaler-hpa-5878b57d96-fvrm7     2/2     Running    1          24m
controller-7479cc984d-m7dxh         2/2     Running    1          24m
istio-webhook-64b48869b8-nmckd      2/2     Running    1          24m
networking-istio-7bb58f6d55-2hlgw   1/1     Running    0          24m
storage-version-migration-bcq59     1/2     NotReady   2          24m
webhook-bf465f954-2nbq9             2/2     Running    1          24m

Environment:

• Istio Version:

$ istioctl version
client version: 1.6.4
control plane version: 1.6.4
data plane version: 1.6.4 (10 proxies)

• Knative Version:

v0.15.0

• KFServing Version:

$ kubectl get KnativeServing knative-serving -n knative-serving
NAME              VERSION   READY   REASON
knative-serving   0.15.0    True

• Kubeflow version: NA

• Kfdef:[k8s_istio/istio_dex/gcp_basic_auth/gcp_iap/aws/aws_cognito/ibm] NA

• Minikube version:

$ minikube  version
minikube version: v1.11.0
commit: 57e2f55f47effe9ce396cea42a1e0eb4f611ebbd

• Kubernetes version: (use kubectl version):

$ kubectl version
Client Version: version.Info{Major:"1", Minor:"18", GitVersion:"v1.18.5", GitCommit:"e6503f8d8f769ace2f338794c914a96fc335df0f", GitTreeState:"clean", BuildDate:"2020-06-26T03:47:41Z", GoVersion:"go1.13.9", Compiler:"gc", Platform:"windows/amd64"}
Server Version: version.Info{Major:"1", Minor:"18", GitVersion:"v1.18.3", GitCommit:"2e7996e3e2712684bc73f0dec0200d64eec7fe40", GitTreeState:"clean", BuildDate:"2020-05-20T12:43:34Z", GoVersion:"go1.13.9", Compiler:"gc", Platform:"linux/amd64"}
``
- OS (e.g. from `/etc/os-release`):
```sh
Edition          Windows 10 Enterprise
Version             1903
Installed on       24/01/2020
OS build            18362.778

[yuzisun]

released in 0.4.1

[yuzisun]

@kmr0877 you are on kubernetes 1.18 and looks like this is the same issue as https://github.com/GoogleCloudPlatform/flink-on-k8s-operator/issues/210, if you downgrade to 1.17 that should work. We will need to upgrade k8s client dependency for KFServing controller.