fix(git): add vendor in .gitignore

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

@@ -1,12 +0,0 @@
-// Copyright 2017 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.
-
-//go:build appengine
-// +build appengine
-
-package gin
-
-func init() {
-	defaultAppEngine = true
-}