Failed to install gems via Bundler　Herokuへデプロイできない(Rails Tutorial　7章)

git push heroku を行ってもHerokuへデプロイ出来ません。
Failed to install gems via Bundler.というエラーメッセージが出てしまい、
自分自身で調べて見た所多くの情報に原因はherokuではsqlite3を使えず本番とローカル環境でDBを切り分けるようGemfileの更新が必要とありましたが、
gemfileにて既に分かれているのにエラーが出てしまいます。
原因は他になにが考えられるんでしょうか？

またその他にconfig/database.ymlのproductionの部分を
production:
<<: *default
adapter: postgresql
encoding: unicode
pool: 5
という書き換えが必要という記事も拝見したためおないましたがダメでした、、、

コード

```source 'https://rubygems.org'

gem 'rails',        '5.1.6'
gem 'bcrypt',         '3.1.12'
gem 'bootstrap-sass', '3.3.7'
gem 'puma',         '3.9.1'
gem 'sass-rails',   '5.0.6'
gem 'uglifier',     '3.2.0'
gem 'coffee-rails', '4.2.2'
gem 'jquery-rails', '4.3.1'
gem 'turbolinks',   '5.0.1'
gem 'jbuilder',     '2.7.0'

group :development, :test do
  gem 'sqlite3', '1.3.13'
  gem 'byebug',  '9.0.6', platform: :mri
end

group :production do
  gem 'pg', '1.1.4'
end


group :development do
  gem 'web-console',           '3.5.1'
  gem 'listen',                '3.1.5'
  gem 'spring',                '2.0.2'
  gem 'spring-watcher-listen', '2.0.1'
end

group :test do
  gem 'rails-controller-testing', '1.0.2'
  gem 'minitest',                 '5.10.3'
  gem 'minitest-reporters',       '1.1.14'
  gem 'guard',                    '2.13.0'
  gem 'guard-minitest',           '2.4.4'
end

# Windows環境ではtzinfo-dataというgemを含める必要があります
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

mi:~/environment/sample_app
1Counting objects: 1314, done.
2Compressing objects: 100% (1282/1282), done.
3Writing objects: 100% (1314/1314), 5.78 MiB | 1.59 MiB/s, done.
4Total 1314 (delta 1008), reused 0 (delta 0)
5remote: Compressing source files... done.
6remote: Building source:
7remote: 
8remote: -----> Ruby app detected
9remote: -----> Compiling Ruby/Rails
10remote: -----> Using Ruby version: ruby-2.4.5
11remote: -----> Installing dependencies using bundler 2.0.1
12remote:        Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin -j4 --deployment
13remote:        Activating bundler (< 2) failed:
14remote:        Could not find 'bundler' (< 2) - did find: [bundler-2.0.1]
15remote:        Checked in 'GEM_PATH=vendor/bundle/ruby/2.4.0', execute `gem env` for more information
16remote:        
17remote:        To install the version of bundler this project requires, run `gem install bundler -v '< 2'`
18remote:        Bundler Output: Activating bundler (< 2) failed:
19remote:        Could not find 'bundler' (< 2) - did find: [bundler-2.0.1]
20remote:        Checked in 'GEM_PATH=vendor/bundle/ruby/2.4.0', execute `gem env` for more information
21remote:        
22remote:        To install the version of bundler this project requires, run `gem install bundler -v '< 2'`
23remote: 
24remote:  !
25remote:  !     Failed to install gems via Bundler.
26remote:  !
27remote:  !     Push rejected, failed to compile Ruby app.
28remote: 
29remote:  !     Push failed
30remote: Verifying deploy...
31remote: 
32remote: !       Push rejected to morning-headland-86878.
33remote: 
34To https://git.heroku.com/morning-headland-86878.git
35 ! [remote rejected]   master -> master (pre-receive hook declined)
36error: failed to push some refs to 'https://git.heroku.com/morning-headland-86878.git'
37コード