* Update deps for release v0.20.0
* Update version command
* Update CHANGELOG
* Run tests against serving and eventing v0.20.0
* Run tests against serving and eventing v0.20.0
* Pin pkg to release-0.18 version
* ./hack/update-deps.sh --upgrade && ./hack/update-codegen.sh
* bump k8s version to 1.18.8
* Fix the brokerage of importing latest serving
* exclude script/test-infra md from md check