fix(git): add vendor in .gitignore

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

@@ -1,16 +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.
-
-package gin
-
-import "net/http"
-
-// CreateTestContext returns a fresh engine and context for testing purposes
-func CreateTestContext(w http.ResponseWriter) (c *Context, r *Engine) {
-	r = New()
-	c = r.allocateContext()
-	c.reset()
-	c.writermem.reset(w)
-	return
-}