Fix GCS

Signed-off-by: Olivier Gambier <olivier@docker.com>

vendor/google.golang.org/appengine/README.md

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+# Go App Engine packages
+
+[![Build Status](https://travis-ci.org/golang/appengine.svg)](https://travis-ci.org/golang/appengine)
+
+This repository supports the Go runtime on App Engine,
+including both classic App Engine and Managed VMs.
+It provides APIs for interacting with App Engine services.
+Its canonical import path is `google.golang.org/appengine`.
+
+See https://cloud.google.com/appengine/docs/go/
+for more information.
+
+File issue reports and feature requests on the [Google App Engine issue
+tracker](https://code.google.com/p/googleappengine/issues/entry?template=Go%20defect).
+
+## Directory structure
+The top level directory of this repository is the `appengine` package. It
+contains the
+basic APIs (e.g. `appengine.NewContext`) that apply across APIs. Specific API
+packages are in subdirectories (e.g. `datastore`).
+
+There is an `internal` subdirectory that contains service protocol buffers,
+plus packages required for connectivity to make API calls. App Engine apps
+should not directly import any package under `internal`.
+
+## Updating a Go App Engine app
+
+This section describes how to update a traditional Go App Engine app to use
+these packages.
+
+### 1. Update YAML files (Managed VMs only)
+
+The `app.yaml` file (and YAML files for modules) should have these new lines added:
+```
+vm: true
+```
+See https://cloud.google.com/appengine/docs/go/modules/#Go_Instance_scaling_and_class for details.
+
+### 2. Update import paths
+
+The import paths for App Engine packages are now fully qualified, based at `google.golang.org/appengine`.
+You will need to update your code to use import paths starting with that; for instance,
+code importing `appengine/datastore` will now need to import `google.golang.org/appengine/datastore`.
+You can do that manually, or by running this command to recursively update all Go source files in the current directory:
+(may require GNU sed)
+```
+sed -i '/"appengine/{s,"appengine,"google.golang.org/appengine,;s,appengine_,appengine/,}' \
+  $(find . -name '*.go')
+```
+
+### 3. Update code using deprecated, removed or modified APIs
+
+Most App Engine services are available with exactly the same API.
+A few APIs were cleaned up, and some are not available yet.
+This list summarises the differences:
+
+* `appengine.Context` has been replaced with the `Context` type from `golang.org/x/net/context`.
+* Logging methods that were on `appengine.Context` are now functions in `google.golang.org/appengine/log`.
+* `appengine.Timeout` has been removed. Use `context.WithTimeout` instead.
+* `appengine.Datacenter` now takes a `context.Context` argument.
+* `datastore.PropertyLoadSaver` has been simplified to use slices in place of channels.
+* `delay.Call` now returns an error.
+* `search.FieldLoadSaver` now handles document metadata.
+* `urlfetch.Transport` no longer has a Deadline field; set a deadline on the
+  `context.Context` instead.
+* `aetest` no longer declares its own Context type, and uses the standard one instead.
+* `taskqueue.QueueStats` no longer takes a maxTasks argument. That argument has been
+  deprecated and unused for a long time.
+* `appengine.BackendHostname` and `appengine.BackendInstance` were for the deprecated backends feature.
+  Use `appengine.ModuleHostname`and `appengine.ModuleName` instead.
+* Most of `appengine/file` and parts of `appengine/blobstore` are deprecated.
+  Use [Google Cloud Storage](https://godoc.org/google.golang.org/cloud/storage) instead.
+* `appengine/socket` is not required on Managed VMs. Use the standard `net` package instead.