Update vendor dependencies

vendor/google.golang.org/appengine/delay/delay_pre17.go

@@ -0,0 +1,19 @@
+// 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 (
+	"reflect"
+
+	"golang.org/x/net/context"
+)
+
+var contextType = reflect.TypeOf((*context.Context)(nil)).Elem()
+
+func isContext(t reflect.Type) bool {
+	return t == contextType
+}