Upgrade go-autorest to 9.1.0

vendor/github.com/Azure/go-autorest/autorest/retriablerequest.go

@@ -1,5 +1,19 @@
 package autorest
 
+// Copyright 2017 Microsoft Corporation
+//
+//  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.
+
 import (
 	"bytes"
 	"io"