Railsチュートリアルのherokuにデプロイ(git push heroku master)でremote rejectedってなった時

Railsチュートリアルの1.5.2章

エラーメッセージ

❯ git push heroku master
Enumerating objects: 94, done.
Counting objects: 100% (94/94), done.
Delta compression using up to 4 threads.
Compressing objects: 100% (77/77), done.
Writing objects: 100% (94/94), 20.94 KiB | 765.00 KiB/s, done.
Total 94 (delta 6), reused 0 (delta 0)
remote: Compressing source files... done.
remote: Building source:
remote:
remote:  !     Warning: Multiple default buildpacks reported the ability to handle this app. The first buildpack in the list below will be used.
remote:                         Detected buildpacks: Ruby,Node.js
remote:                         See https://devcenter.heroku.com/articles/buildpacks#buildpack-detect-order
remote: -----> Ruby app detected
remote:
remote:  !
remote:  !     You must use Bundler 2 or greater with this lockfile.
remote:  !

〜〜〜〜　省略　〜〜〜〜

 ! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'https://git.heroku.com/アプリ名.git'

解決方法

❯ bundle version
Bundler version 2.0.1 (2019-01-04 commit d7ad2192f)

❯ gem uninstall bundler -v 2.0.1
Successfully uninstalled bundler-2.0.1

❯ rm -f Gemfile.lock

❯ bundle install

❯ git add Gemfile.lock

❯ git add commit

❯ git push

❯ git push heroku master  # 成功