herokuにpushしたいがFailed to install gems via Bundlerエラーが起き失敗する

###現状
作成したアプリをherokuにpushするためにこのページを元に作業を進めていたところ、
git push heroku masterを実行した時にタイトルのエラーが起きました。

###ログ

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: -----> Compiling Ruby/Rails
remote: -----> Using Ruby version: ruby-2.6.3
remote: -----> Vendoring libpq 5.12.1
remote: -----> Removing BUNDLED WITH version in the Gemfile.lock
remote: -----> Installing dependencies using bundler 1.17.3
remote:        Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin -j4 --deployment
remote:        You are trying to install in deployment mode after changing
remote:        your Gemfile. Run `bundle install` elsewhere and add the
remote:        updated Gemfile.lock to version control.
remote:        
remote:        The dependencies in your gemfile changed
remote:        
remote:        You have added to the Gemfile:
remote:        * sqlite3 (~> 1.3.6)
remote:        
remote:        You have deleted from the Gemfile:
remote:        * sqlite3
remote:        Bundler Output: You are trying to install in deployment mode after changing
remote:        your Gemfile. Run `bundle install` elsewhere and add the
remote:        updated Gemfile.lock to version control.
remote:        
remote:        The dependencies in your gemfile changed
remote:        
remote:        You have added to the Gemfile:
remote:        * sqlite3 (~> 1.3.6)
remote:        
remote:        You have deleted from the Gemfile:
remote:        * sqlite3
remote: 
remote:  !
remote:  !     Failed to install gems via Bundler.
remote:  !
remote:  !     Push rejected, failed to compile Ruby app.
remote: 
remote:  !     Push failed
remote: Verifying deploy...
remote: 
remote: !       Push rejected to kakeibo009.

###試したこと
Failed to install gems via Bundler.の箇所からbundlerに原因が
あることは分かるのですが、解決法が見つかりませんでした。
buildpackの方に問題があるのでしょうか。
###補足
GemfileとGemfile.lockのBUNDLED WITHは両方とも2.0.1
Bundlerのバージョンは 2.0.1でした

database.ymlはこの状態です。

DatabaseYML
1# SQLite version 3.x
2#   gem install sqlite3
3#
4#   Ensure the SQLite 3 gem is defined in your Gemfile
5#   gem 'sqlite3'
6#
7default: &default
8  adapter: sqlite3
9  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
10  timeout: 5000
11
12development:
13  <<: *default
14  database: db/development.sqlite3
15
16# Warning: The database defined as "test" will be erased and
17# re-generated from your development database when you run "rake".
18# Do not set this db to the same as development or production.
19test:
20  <<: *default
21  database: db/test.sqlite3
22
23production:
24  <<: *default
25  adapter: postgresql
26  encoding: unicode
27  pool: 5
28  
29