Pin github.com/googleapis/gnostic to v0.4.0

See https://github.com/google/gnostic/pull/155

vendor/gopkg.in/yaml.v3/NOTICE

@@ -1,13 +0,0 @@
-Copyright 2011-2016 Canonical Ltd.
-
-Licensed under the Apache License, Version 2.0 (the "License");
-you may not use this file except in compliance with the License.
-You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-See the License for the specific language governing permissions and
-limitations under the License.