use go1.11 with go mod

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

@@ -1,21 +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 render
-
-import (
-	"encoding/xml"
-	"net/http"
-)
-
-type XML struct {
-	Data interface{}
-}
-
-var xmlContentType = []string{"application/xml; charset=utf-8"}
-
-func (r XML) Render(w http.ResponseWriter) error {
-	writeContentType(w, xmlContentType)
-	return xml.NewEncoder(w).Encode(r.Data)
-}