use go1.11 with go mod

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

@@ -1,12 +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 gin
-
-import "log"
-
-func (c *Context) GetCookie(name string) (string, error) {
-	log.Println("GetCookie() method is deprecated. Use Cookie() instead.")
-	return c.Cookie(name)
-}