use go1.11 with go mod

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

@@ -1,31 +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 "net/http"
-
-type Render interface {
-	Render(http.ResponseWriter) error
-}
-
-var (
-	_ Render     = JSON{}
-	_ Render     = IndentedJSON{}
-	_ Render     = XML{}
-	_ Render     = String{}
-	_ Render     = Redirect{}
-	_ Render     = Data{}
-	_ Render     = HTML{}
-	_ HTMLRender = HTMLDebug{}
-	_ HTMLRender = HTMLProduction{}
-	_ Render     = YAML{}
-)
-
-func writeContentType(w http.ResponseWriter, value []string) {
-	header := w.Header()
-	if val := header["Content-Type"]; len(val) == 0 {
-		header["Content-Type"] = value
-	}
-}