Use Go1.11 module (#5743)

* Migrate to go modules

* make vendor

* Update mvdan.cc/xurls

* make vendor

* Update code.gitea.io/git

* make fmt-check

* Update github.com/go-sql-driver/mysql

* make vendor

vendor/google.golang.org/appengine/cloudsql/cloudsql_vm.go

@@ -0,0 +1,16 @@
+// Copyright 2013 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 !appengine
+
+package cloudsql
+
+import (
+	"errors"
+	"net"
+)
+
+func connect(instance string) (net.Conn, error) {
+	return nil, errors.New(`cloudsql: not supported in App Engine "flexible environment"`)
+}