vendor: add github.com/diegomarangoni/gcscache

also include all transitive dependencies of gcscache, which seems to
bring in the entire world of Google Cloud Platform.

vendor/cloud.google.com/go/storage/go110.go

@@ -0,0 +1,30 @@
+// Copyright 2017 Google Inc. All Rights Reserved.
+//
+// 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.
+
+// +build go1.10
+
+package storage
+
+import "google.golang.org/api/googleapi"
+
+func shouldRetry(err error) bool {
+	switch e := err.(type) {
+	case *googleapi.Error:
+		// Retry on 429 and 5xx, according to
+		// https://cloud.google.com/storage/docs/exponential-backoff.
+		return e.Code == 429 || (e.Code >= 500 && e.Code < 600)
+	default:
+		return false
+	}
+}