Fix fragment in schema URL

Also switched to a particular tag in the spec repo.
Also called out the minor release number in the text of the reference.

Signed-off-by: Mike Spreitzer <[email protected]>

Author: MikeSpreitzer

content/en/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions.md

@@ -579,7 +579,7 @@ deleted by Kubernetes.
 ### Validation
 
 Custom resources are validated via
-[OpenAPI v3 schemas](https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.0.md#schemaObject),
+[OpenAPI v3.0 schemas](https://github.com/OAI/OpenAPI-Specification/blob/3.0.0/versions/3.0.0.md#schema-object),
 by x-kubernetes-validations when the [Validation Rules feature](#validation-rules) is enabled, and you
 can add additional validation using
 [admission webhooks](/docs/reference/access-authn-authz/admission-controllers/#validatingadmissionwebhook).