use go1.11 with go mod

vendor/github.com/gin-gonic/gin/binding/xml.go

@@ -1,24 +0,0 @@
-// Copyright 2014 Manu Martinez-Almeida.  All rights reserved.
-// Use of this source code is governed by a MIT style
-// license that can be found in the LICENSE file.
-
-package binding
-
-import (
-	"encoding/xml"
-	"net/http"
-)
-
-type xmlBinding struct{}
-
-func (xmlBinding) Name() string {
-	return "xml"
-}
-
-func (xmlBinding) Bind(req *http.Request, obj interface{}) error {
-	decoder := xml.NewDecoder(req.Body)
-	if err := decoder.Decode(obj); err != nil {
-		return err
-	}
-	return validate(obj)
-}