fix(git): add vendor in .gitignore

vendor/google.golang.org/api/internal/gensupport/doc.go

@@ -1,10 +0,0 @@
-// Copyright 2016 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// Package gensupport is an internal implementation detail used by code
-// generated by the google-api-go-generator tool.
-//
-// This package may be modified at any time without regard for backwards
-// compatibility. It should not be used directly by API users.
-package gensupport