Update vendor dependencies

vendor/google.golang.org/appengine/delay/delay_go17.go

@@ -0,0 +1,23 @@
+// Copyright 2017 Google Inc. All rights reserved.
+// Use of this source code is governed by the Apache 2.0
+// license that can be found in the LICENSE file.
+
+//+build go1.7
+
+package delay
+
+import (
+	stdctx "context"
+	"reflect"
+
+	netctx "golang.org/x/net/context"
+)
+
+var (
+	stdContextType = reflect.TypeOf((*stdctx.Context)(nil)).Elem()
+	netContextType = reflect.TypeOf((*netctx.Context)(nil)).Elem()
+)
+
+func isContext(t reflect.Type) bool {
+	return t == stdContextType || t == netContextType
+}