Update vendor dependencies

vendor/golang.org/x/net/http2/not_go18.go

@@ -0,0 +1,18 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !go1.8
+
+package http2
+
+import "net/http"
+
+func configureServer18(h1 *http.Server, h2 *Server) error {
+	// No IdleTimeout to sync prior to Go 1.8.
+	return nil
+}
+
+func shouldLogPanic(panicValue interface{}) bool {
+	return panicValue != nil
+}